0:00 [Music]
0:03 when you look at the night sky you can
0:06 see thousands of stars using nothing but
0:09 your eyes far from the lights of cities
0:14 in fact there are many more stars in the
0:16 sky which are too faint for us to see
0:20 every single star that you can see is a
0:22 part of our Milky Way galaxy our
0:25 Heavenly home that has captured people's
0:27 attention for ages
0:30 the shimmering band of stars dust gas
0:34 and dark matter that makes up the night
0:36 sky captures our attention these
0:40 elements are all held together by
0:43 gravity as we navigate through the
0:45 cosmos an intriguing Enigma emerges what
0:49 is the Milky Way truly like what makes
0:53 it up and where does our solar system
0:55 exist in the Milky
0:58 Way astronomers have been been baffled
1:00 by these fundamental questions for many
1:02 centuries and finding answers was no
1:06 easy
1:07 task but beyond its luminous beauty lies
1:11 a tapestry of mysteries waiting to be
1:14 unraveled join us today as we embark on
1:18 an amazing adventure around the Milky
1:20 Way uncovering its Mysteries wonders and
1:23 Majesty
1:34 [Music]
1:35 you're probably somewhat familiar with
1:38 our solar system if nothing else you
1:41 probably already know that it contains
1:43 eight planets in addition to the Earth
1:46 the Sun moons and several other
1:49 celestial bodies like asteroids and
1:53 Pluto however there is a lot more beyond
1:56 the solar system of which you may not be
1:58 aware
2:01 from Earth we can see roughly 6,000
2:05 stars without the use of a telescope
2:08 even while that seems like a large
2:09 number of stars it represents a very
2:12 small portion of the total in fact for
2:15 every Star you can see there are more
2:17 than 20 million you cannot see the
2:21 majority of stars are either too dim too
2:23 far or obstructed by clouds of cosmic
2:28 dust while the Milky Way galaxy contains
2:31 all of these stars there are other
2:33 larger galaxies as well including the
2:36 Andromeda
2:38 galaxy every Galaxy is a system made up
2:41 of various Stellar remnants interstellar
2:43 medium and star
2:46 systems astronomers believe there are
2:48 100 billion galaxies in the cosmos yet
2:51 they are not sure Intergalactic space
2:54 which contains a thin gas lies in
2:57 between the galaxies given the size of
3:00 our solar system and the fact that it is
3:02 only one of many in our galaxy it is
3:05 understandable why the universe is
3:07 thought to be infinite This truly helps
3:09 to put into perspective how tiny both
3:13 Earth and humans are in the big
3:17 picture through the use of radio and
3:19 x-ray telescopes scientists have been
3:22 able to gather information during the
3:24 past Century about the composition of
3:27 the interstellar medium they have shown
3:30 that it is made up of extremely diffuse
3:32 ionized hydrogen atoms dust and cosmic
3:36 rays scattered throughout thick gas
3:38 clouds that are thought to be the
3:40 birthplace of new
3:44 stars but because of the sun all eight
3:48 planets and a far off disc of debris
3:51 known as the Kyer belt its precise
3:54 nature just outside our solar system has
3:57 remained mostly unknown
4:00 the Kyper Belt is located between 30 and
4:02 50 astronomical units from the Sun one
4:07 astronomical unit is equivalent to the
4:09 distance between Earth and the
4:11 Sun the heliosphere a massive protective
4:15 bubble created by the solar wind
4:18 surrounds them all this bubble buffets
4:21 against the interstellar medium like an
4:24 invisible shield keeping out most
4:26 dangerous cosmic rays and other material
4:29 as the sun and its surrounding planets
4:32 hurtle across the
4:34 Galaxy without the heliosphere life
4:37 would certainly have evolved differently
4:40 and maybe not at
4:43 all the area where the sun's magnetic
4:46 bubble ends and weakens is known as the
4:49 interstellar Space
4:51 Border the heliosphere a magnetic bubble
4:54 is full of plasma or ionized gas the
4:58 solar wind which pulls magnetic field
5:01 lines away from the Sun blows material
5:04 into the
5:05 heliosphere with its own magnetic fields
5:07 and charged particles the plasma in the
5:10 interstellar medium exerts an inward
5:13 push on the heliosphere Edge creating a
5:17 complex and dynamic structure there when
5:20 the solar wind encounters Interstellar
5:22 space it begins to weaken and slows to
5:25 approximately 62
5:28 mph it was previously traveling between
5:31 370 and 430
5:34 mph the termination shock is the point
5:38 at which this happens the Helios Heath
5:41 is the area in the heliosphere where the
5:43 solar wind continues to slow down after
5:47 the termination shock while the
5:49 heliopause is the outermost point of the
5:53 heliosphere the solar wind stops and
5:56 gives way to Interstellar space at the
5:58 Helia pores which is located around 11
6:01 billion mil or 18 billion km from the
6:06 [Music]
6:07 Sun 5 4 3 2
6:13 1 we have ignition we have a left
6:17 off since the beginning of human space
6:20 exploration only two probes have made it
6:23 to Interstellar space or the area
6:26 outside of the solar
6:28 system after launch in
6:30 1977 Voyager 1 the first spacecraft took
6:34 more than 30 years to reach the Helia
6:37 por a limit that scientists believe
6:40 marks the beginning of interstellar
6:42 space it was an amazing accomplishment
6:46 sending back Vital Information via a
6:49 medium unaffected by the
6:53 Sun as we exit the solar system we will
6:57 reach Alpha centor the triple star
7:00 system which is the closest star system
7:03 to Earth located at about 4.37 light
7:07 years away in the constellation
7:09 Centaurus it is a triple star system
7:12 consisting of three stars Alpha centu a
7:16 alpha centor B and Proxima centor Alpha
7:20 centor AB is a binary star system made
7:24 up of alpha centu A and B which are
7:27 sunlike stars classified as class plus G
7:29 and K
7:31 respectively these two main stars have
7:33 an apparent magnitude of-
7:36 0.27 making them appear to be a single
7:39 star to the uned
7:42 eye only Sirius and canopus are brighter
7:45 than it making it the brightest star in
7:48 the constellation and the third
7:50 brightest in the night
7:52 sky Alpha centor B is smaller and colder
7:57 than Alpha centor a with z 0.9 solar
8:00 mass and less than
8:02 0.5 solar
8:05 Luminosity while Alpha centor a has 1.5
8:08 times the luminosity and 1.1 time the
8:11 mass of the Sun the two have a 79-year
8:14 orbital period around a shared Center
8:17 the distance between A and B fluctuates
8:20 from 35.6 astronomical units or roughly
8:24 the distance between Pluto and the sun
8:26 to 11.2 Au or rough the distance between
8:30 Saturn and the sun due to the
8:32 eccentricity of their elliptical
8:36 orbit in the alpha centor system Proxima
8:40 centor is the star nearest to the sun
8:43 located approximately 4.2 light years
8:46 from Earth Robert inis a Scottish
8:50 astronomer made the discovery of the
8:52 star in
8:54 195 Proxima centor is a red dwarf star
8:59 which is the the most common kind of
9:00 star it is roughly seven times smaller
9:03 than the Sun and a little more than half
9:06 as hot at
9:07 3,100 Kelvin on the other hand our sun
9:11 is
9:13 5,772 Kelvin as a matter of fact this
9:17 little star is just 50% larger than
9:22 Jupiter red dwarf stars have long lives
9:25 because they consume hydrogen fuel very
9:28 efficiently Proxima centor is expected
9:31 to remain in its current state for more
9:34 than 4 trillion
9:37 years although the alpha centor system
9:39 can be seen in the constellation
9:41 Centaurus Proxima centor is usually not
9:44 visible to the human eye Proxima centor
9:48 orbits the other two stars in the system
9:51 Alpha centor A and
9:54 B Proxima centor takes 550,000 years to
9:59 complete an orbit of A and B with an
10:02 apparent visual magnitude of 11 Proxima
10:05 centor is the Diest of the three
10:09 stars this star emits light at a slower
10:12 rate than the sun with a Luminosity of
10:15 0.17% that of the
10:17 sun however Proxima centori is
10:20 categorized as a flare star which is
10:23 prone to massive solar flares because
10:25 its brightness can vary by more than one
10:28 magnitude in a matter of
10:31 minutes these flares which occur
10:33 multiple times a day have the potential
10:36 to be powerful enough to make Proxima
10:39 centor visible to the human
10:42 eye the greatest solar flare ever
10:45 observed in the Milky Way galaxy was
10:48 released by Proxima centori in
10:51 2019 glowing 14,000 times brighter in
10:55 ultraviolet wavelengths than normal
10:59 even though Proxima centori will live
11:02 longer than the sun it will eventually
11:04 meet the same fate Proxima centor will
11:08 end up as a burning white dwarf star
11:12 because it does not have the mass to
11:14 turn into a neutron star or a black hole
11:17 when its hydrogen Supply runs
11:21 out as of 2022 astronomers have detected
11:25 three planets orbiting Proxima
11:27 centor Proxima
11:29 b c and
11:31 d these are the closest planets outside
11:34 the solar
11:35 system red dwarf stars are small and
11:38 cool thus planets can Circle quite close
11:41 to them and still be classified as being
11:44 in the habitable
11:46 zone this is the range of distance from
11:49 a star where a planet's water if any
11:52 could be liquid and potentially support
11:55 life Proxima centor B was discovered in
11:58 2016
12:00 and estimated the planet to contain
12:01 about 177% more mass than Earth and thus
12:06 likely to be a rocky planet as well
12:09 Proxima centor B is still within Proxima
12:12 Cent's habitable zone despite being far
12:15 closer to its star than Earth is to the
12:18 sun it orbits Proxima centor every 11
12:22 Earth days at a distance of about
12:25 0.049 Au over 20 times closer to Proxima
12:30 centor than Earth is to the sun Proxima
12:33 centor B is most likely tidily locked
12:36 like our moon with one side always
12:39 facing Earth given that it is far closer
12:42 to its star than
12:44 Earth it is therefore possible that
12:46 liquid water exists on the opposite side
12:49 but its habitability is unknown due to
12:52 the extreme radiation and flares from
12:54 its host
12:56 star Proxima centor B feel the
12:59 gravitational pull of Their Stars much
13:03 more strongly than we feel the tidal
13:05 effect of our
13:06 sun here on Earth the moon exerts more
13:10 tidal Force Than The Sun Also because
13:13 it's so much closer and Tides don't just
13:16 pull on the ocean they can also move
13:19 air it's possible that the tidal pool on
13:22 the atmosphere of Proxima centor B is up
13:25 to 500 times stronger than that of
13:28 Earth's at
13:30 atmosphere it's likely that Proxima
13:32 centor B is getting close to the maximum
13:35 tidal force that a planet can withstand
13:38 and still retain a solid
13:42 surface however Proxima centor be's
13:45 climate and weather are mostly
13:47 unaffected by its extremely high
13:53 tides situated just outside of the
13:55 habitable zone at around 1.5
13:58 astronomical units from the Red Dwarf is
14:01 the mini Neptune exoplanet Proxima
14:03 centori CA which is around seven times
14:07 the size of Earth and orbits its star
14:10 once every
14:12 1,900 Earth
14:15 days first thought to have been
14:17 discovered in 2019 the superar planet it
14:21 appears to shine much brighter than
14:23 expected for that size indicating that
14:26 it may be shrouded in dust clouds or
14:29 circled by a ring system the projected
14:32 planet's estimated temperature by
14:33 astronomers is extremely cold probably
14:36 close to -
14:38 233°
14:40 c this makes it uninhabitable due to its
14:43 distance from its star and large
14:47 mass the gravitational pool of Proxima
14:50 centor sea caused its parent Stars
14:53 velocity to wobble which led to the
14:55 star's initial detection in 2019
14:59 in 2020 pictures from the Hubble Space
15:02 Telescope from
15:03 1995 were used to confirm Proxima centor
15:07 SE existence it is therefore one of the
15:09 rare exoplanets with visual
15:13 confirmation a third planet was
15:15 discovered in 2022 around Proxima centor
15:19 the exoplanet known as Proxima centor D
15:23 orbits its star at a distance of roughly
15:25 3% of Earth's distance from the Sun and
15:29 contains about 25% of Earth's mass every
15:33 five Earth days Proxima centor D
15:37 completes one orbit around its star due
15:40 to its relative proximity to
15:43 it it is among the lightest exoplanets
15:46 that scientists have yet
15:48 observed furthermore in 2021 scientists
15:53 detected what may be the first
15:55 indications of an exoplanet circling
15:58 Alpha Cent a also known as rigil curus
16:03 in the Stars habitable zone called
16:05 candidate C1 it is estimated that C1 has
16:09 a mass between half of Saturn and
16:10 Neptune and orbits Alpha centor a at a
16:14 distance of roughly 1.1
16:17 Au using direct thermal imaging C1 was
16:21 found with an elongation of around 0.1
16:25 Arc it looks to be as bright as a giant
16:28 planet
16:29 this is consistent with the orbital
16:31 motion of a planet in a 70°
16:34 orbit the fact that C1 is situated in
16:37 the habitable zone of alpha centor a and
16:40 maybe a mini Neptune or super earth
16:43 makes the discovery of this exoplanet
16:46 much more
16:49 interesting we are almost certain that
16:51 planets similar to Earth exist in Alpha
16:55 centor but the main question is could
16:57 humans ever actually live
16:59 [Music]
17:01 there the most challenging obstacle in
17:03 our quest to set up a new home in the
17:05 alpha centor system would undoubtedly be
17:08 traveling a huge distance to reach these
17:11 three
17:12 stars even though Alpha centori is the
17:15 nearest star system to Earth it is still
17:17 more than four light years away that
17:20 comes to roughly 23.5 trillion miles or
17:23 37.8 trillion
17:26 km we would need a far faster spacecraft
17:29 or another means of transportation to
17:31 cover such a great
17:34 distance NASA claims that the Space
17:36 Shuttle Discovery which was discontinued
17:39 in 2011 had a top speed of about
17:43 17,500 m per
17:46 hour still reaching Alpha centor would
17:49 take more than 148,000 years even at
17:53 this steady
17:55 speed NASA estimates that even when the
17:58 Orion spacecraft the crew capsule linked
18:01 to the Artemis program is prepared to
18:04 carry people its maximum velocity will
18:07 be approximately 20,000
18:09 mph this won't significantly cut down
18:12 this travel time to Proxima
18:14 centori that's even if either of these
18:17 vehicles was designed to Journey out of
18:19 the solar system rather than just making
18:21 relatively short trips to the moon or
18:26 Mars as we have already disc discussed
18:29 the only spacecraft to make it out of
18:31 the solar system thus far are Voyager 1
18:34 and two even at their top speed of over
18:37 35,000 mph it will take them nearly
18:41 40,000 years to travel two light years
18:44 to reach the indistinct boundary between
18:47 Proxima centor and our solar
18:50 system that implies that it might take
18:53 these spacecraft more than 880,000 years
18:56 to reach close to the star
19:00 after all it takes light more than four
19:02 years to reach Alpha
19:04 centori a spacecraft needs to be
19:07 extremely tiny and robotic in order to
19:10 reach a distant star in a reasonable
19:12 amount of time like within a
19:15 generation furthermore it still needs an
19:18 incredibly strong energy boost to get up
19:20 to
19:22 speed and that is the basic concept
19:26 behind the Breakthrough star shot
19:27 project by creating a light sale
19:30 equipped nanocraft called star chip that
19:34 would be sent into Earth orbit the
19:37 Mother Ship would release the tiny
19:39 probes one at a time which would then
19:42 ride the beams of a colossal groundbased
19:45 laser array the main challenge though is
19:49 the Earth's atmosphere which distorts
19:52 laser and incoming light and makes it
19:54 challenging to apply the force required
19:57 to move a spacecraft
19:59 forward much more potent lasers on the
20:02 ground would be able to keep a close
20:04 focus on the space mission thanks to
20:06 small lasers mounted on satellites that
20:10 would evaluate atmospheric impacts in
20:13 real
20:14 time to send out the vessel at any given
20:17 time the required lasers need an
20:20 astounding 100 gaw of power which is
20:23 equal to the total us electricity
20:26 usage but the lasers only need to
20:29 operate for 10 minutes at full power
20:32 they plan to employ 100 million lasers
20:36 to distribute the electricity across an
20:38 area of 1 km
20:40 Square the starshot team is determined
20:44 to push the boundaries of space
20:47 exploration when the lasers are Switched
20:49 Off the object racing through space will
20:52 be traveling at a stunning 20% of the
20:55 speed of light more than 130 million
20:58 miles mph or 216 million
21:02 kmph with a diameter of little over 10 m
21:06 this spacecraft could reach to Alpha
21:08 centor in about 22
21:11 years but it might be significantly
21:14 slowed down by the sun's gravitational
21:17 pull and Interstellar
21:19 debris it will take four more years for
21:22 the spacecraft signals to reach Earth
21:26 even if they make it to Alpha centor
21:28 [Music]
21:30 Alpha centori is moving toward Earth but
21:34 very slowly and doesn't pose an
21:36 immediate cause for concern the distance
21:39 between Alpha centor and Earth as of
21:42 2024 is approximately 3.26 light years
21:46 it will be at its closest in
21:49 29,700 ad when it will be approximately
21:53 three light years
21:54 away over the course of a human lifetime
21:57 the slow change in distance will have no
22:00 noticeable impact on Earth or the solar
22:04 system space is a remarkable place we're
22:08 learning new things about it every
22:12 day leaving Alpha centory behind we
22:16 travel on to the Barnard star the second
22:19 nearest star to the Sun at a distance of
22:22 5.95 light years it has the name Edward
22:27 Emerson Barnard in honor of the American
22:30 astronomer who made the discovery in
22:33 1916 with an estimated age of 11 to 12
22:37 billion years or roughly twice that of
22:40 the sun Barnard's star is an old star
22:44 and most likely a thick disc member of
22:45 the Milky
22:47 Way Red dwarfs that are young or
22:50 middle-aged often spin fast enough to
22:53 produce powerful magnetic fields which
22:55 can result in flares that quickly double
22:58 A star's
23:00 brightness but Barnard star was too old
23:03 to show this kind of
23:06 behavior however on July 17th
23:09 1998 Diane pson and her colleagues at
23:12 NASA's godded space flight center
23:14 revealed that a flare similar to this
23:16 one had been released by Barnard
23:19 star at the time the star's Spectra was
23:23 being obtained using the 2.7 M telescope
23:26 at McDonald Observatory by William
23:28 Cochran of the University of Texas at
23:32 Austin his hope had been to find
23:34 Alterations that would point to the
23:36 existence of planets in
23:39 orbit rather he saw emission lines in
23:42 the Spectrum which showed that the star
23:45 might be
23:46 flaring 4 years later Cochran team's
23:50 investigation revealed that the star's
23:53 hot blue flare was similar to those from
23:56 younger red dwarfs even though it was
23:58 quite quite
23:59 old the temperature of the flare was at
24:01 least 8,000 Kelvin which was more than
24:05 twice as hot as the 3,100 kelv
24:08 temperature of the
24:10 Star as Barnard star gets closer to us
24:13 its distance from us is decreasing by
24:17 0.036 light years every Century at an
24:21 incredibly fast speed of 108 km/s or 67
24:26 m/s
24:28 its closest approach to the sun will be
24:31 at a distance of just 3.85 light years
24:34 by
24:35 11,800
24:37 ad in terms of its proper motion Barnard
24:41 star is also the fastest moving star in
24:45 Earth's
24:46 Skies another feature that makes Barnard
24:49 star unique is the largest proper motion
24:52 of any Star which is approximately 10.4
24:55 arcs per year or the equival
24:58 of a lunar diameter every 180 years
25:03 since of this and its relative closeness
25:06 it is an ideal Target for exoplanet
25:09 searches since any systematic variations
25:12 in its motion across the sky brought on
25:15 by planets in orbit would be more
25:18 noticeable finally a planet was found
25:21 around Barnard star in
25:24 2018 the planet orbits the star at a
25:27 distance of roughly 60 million km or 37
25:31 million miles on a 233 day orbit with a
25:36 mass at least 3.2 times that of Earth
25:39 the planet is not in the habitable zone
25:41 due to the Stars low brightness and any
25:44 water on its surface would probably be
25:49 Frozen as we go farther away around 8.6
25:54 light years away near the constellation
25:56 of Orion we will find Sirius also known
26:00 as the dog star or Sirius a which is the
26:04 brightest star in Earth's night sky with
26:07 a mass twice that of the sun Sirius has
26:10 a diameter of 1.5 million miles or 2.4
26:14 million kilm the star Sirius would
26:17 outshine our sun by a factor of more
26:19 than 20 if it were positioned next to it
26:23 within the Kus Major constellation
26:25 Sirius is a binary star
26:28 the star's name comes from the Greek
26:30 word seros which means glowing or
26:34 scorching with a surface temperature of
26:36 almost 18,000 de F Sirius has a bluish
26:41 tint and is 25 times brighter than the
26:44 sun it is clearly visible in the
26:47 winternight sky of the northern
26:49 hemisphere the Ancients were familiar
26:51 with Sirius due of its extreme
26:54 brightness nevertheless astronomers were
26:56 taken aback when serus b a companion
26:59 star was discovered in
27:03 1862 the star is visible to the naked
27:07 eye on the other hand Sirius B is 10,000
27:11 times fainter than
27:14 Sirius thanks to data from the Hubble
27:16 Space Telescope astronomers were finally
27:19 able to estimate the mass of this faint
27:21 object in
27:23 2005 despite the fact that it is
27:26 extremely difficult to observe from
27:27 Earth
27:29 within 20 light years of the sun are
27:32 around 131 objects including Stars Brown
27:37 dwarfs and sub Brown
27:39 dwarfs only 22 stars are bright enough
27:43 to be seen without a telescope meaning
27:46 their visible light must be at least 6.5
27:50 apparent magnitude the lowest brightness
27:53 that can be seen with the naked eye from
27:56 Earth the known 131 objects abound in
28:00 994 Stellar systems out of these 103 are
28:04 main sequence Stars consisting of 23
28:08 typical stars with a higher mass and 80
28:11 red
28:12 dwarfs in addition scientists have
28:15 discovered 21 Brown dwarfs one sub brown
28:19 dwarf Y 0855
28:23 0714 which is possibly a rogue planet
28:26 and six white dwarfs
28:29 white dwarfer stars that have used up
28:31 all of their fusible
28:34 hydrogen a red dwarf candidate known as
28:37 Schultz's star and a companion brown
28:40 dwarf passed near the edge of the art
28:42 cloud around 70,000 years
28:46 ago at this moment it is approximately
28:49 22 light years away from the Sun and has
28:52 likely triggered a comet storm that will
28:54 take over a million years to reach the
28:56 inner solar system
28:59 the Kyer belt object's orbits were
29:01 impacted by its
29:03 passage some other stars such as the
29:06 gtype Star HD
29:08 7977 have also been
29:10 researched it had its close pass around
29:13 2.8 million years ago and it is
29:16 currently located about
29:18 247 light years from Earth of course
29:22 past interactions aren't the only thing
29:24 to consider about there will be more
29:27 stars in the future
29:29 in the next 15 million years 694 stars
29:33 are predicted to approach the solar
29:35 system at a distance of less than 516
29:39 light years Based on data from the Gaia
29:42 telescope's second data release 26 of
29:45 them are likely to arrive within 3.3
29:48 light years and seven more within six
29:52 light
29:53 years due to the sheer number of stars
29:56 that must be surveyed this number is
29:58 probably much higher for example a star
30:01 that was approaching the solar system 10
30:03 million years ago would be 600 to 6,000
30:07 light years away from the Sun today
30:10 whereas millions of stars are now closer
30:13 to the
30:14 Sun glea 710 a star is among the most
30:19 well-known instances of a close future
30:22 passage it is an orange star around 60%
30:26 the size of the sun
30:28 located in the Serpent's
30:31 constellation this star is heading in
30:33 our Direction at a speed of
30:37 5,499 KM hour or almost 32,000
30:42 mph in
30:44 1.29 million years it will pass the Sun
30:48 at a distance of around
30:50 10,520
30:52 Au it's over 100 times the distance to
30:56 Pluto which orbits the Sun
30:58 at an average of 39.5
31:02 au but it still has the potential to
31:05 disrupt the solar
31:07 system if humans are still around on
31:09 Earth at that point we don't have to
31:11 worry about any disruptions to our
31:13 orbit if Gazza 710 has any effect at all
31:17 it might only have it on the outer solar
31:19 system it shouldn't have any impact on
31:22 anything inside 40 astronomical units
31:25 but still it could possibly cause
31:27 disruptions to the art cloud because it
31:30 has a very high probability of going
31:32 through
31:32 it for millions of years Comet showers
31:36 would result from that heading toward
31:39 the sun this might lead to roughly 10
31:42 comets visible to the uned eye every
31:45 year searches for stars that are close
31:48 to the Sun could not only be an
31:50 opportunity of finding ancient comets
31:53 but also of predicting an intriguing
31:55 future for observers on Earth millions
31:58 or even thousands of years from
32:02 now the local Interstellar Cloud which
32:05 is around 30 light years large is where
32:08 the solar system and the other stars and
32:10 dwarfs are now moving within or close to
32:14 it the local Interstellar cloud is in
32:17 turn contained inside the local
32:21 bubble a cavity in the interstellar
32:24 medium about 1,000 light years across
32:28 and has an odd peanut
32:30 shape our sun was far away when the
32:33 bubble first formed 14 million years ago
32:36 but about 5 million years ago the sun's
32:39 path made its way into the
32:42 bubble interestingly star formed on the
32:46 surface of the bubble but not inside it
32:49 there are seven star forming regions
32:51 around this
32:53 bubble because of this local bubble life
32:56 has become possible
32:58 on Earth
33:03 today as we go farther away we will
33:06 reach Orion constellation around 1344
33:10 light years away from Earth one light
33:13 year is the distance light travels in a
33:15 single year about 6 trillion miles or 10
33:19 trillion
33:21 kilm the Orion constellation is one of
33:24 the 88 modern constellations and is
33:26 named after the
33:28 in Greek
33:29 mythology it contains over 60 Stars
33:33 including Beal
33:34 Jews a red super giant Star located at
33:38 around 650 light years away this is one
33:42 of the largest known stars with a
33:44 diameter of about 767 million mil or 1.2
33:49 billion
33:50 km it's about 700 times the size of the
33:54 sun and has a mass between 10 and 20
33:57 times that of the sun because Beatle juw
34:00 may have less than 300 years of fuel
34:02 left in its core there has been
34:05 continuous discussion throughout the
34:07 world on whether or not it would
34:10 explode the Stars core will collapse
34:13 into a black hole as it burns through
34:15 those final drops blasting out the Stars
34:18 outer layers at speeds of up to 25,000
34:22 m/s or 40,000
34:25 km/s astronomers refer to this blazing
34:29 demise as a supernova explosion and in
34:32 Bal ju's case it will be a breathtaking
34:35 sight for observers on Earth those
34:39 layers of gas and dust will shine in our
34:41 sky for several weeks comparable in
34:45 brightness to the full moon because the
34:47 star is only 650 light years away from
34:52 Earth the issue is that most astronomers
34:55 do not think Bal juice is quite ready
34:58 for a big explosion just yet astronomers
35:02 normally expect that it will blow up in
35:04 the next 100,000 years or soon on a
35:08 cosmic time frame not a human
35:12 one the other famous stars in this
35:14 constellation is in the line Orion's
35:17 Belt which consists three stars located
35:20 around the middle of the constellation
35:23 Orion these are alnitak Alan
35:28 and minaka from east to west the belt is
35:32 perhaps the most recognizable feature of
35:34 Orion because it is visible all around
35:37 the
35:38 world these three super giant Stars
35:42 separately a thousands or tens of
35:44 thousands of times brighter and several
35:47 times more massive than the sun despite
35:50 these stars look closer to one another
35:51 in the sky they are actually light as
35:55 apart Orion's belt
35:58 is mainly used by astronomers as a
36:00 Celestial Landmark when searching for
36:03 m42 also known as the Orion
36:08 Nebula m42 is located below the belt and
36:11 is one of the most visible messier
36:13 objects for beginner astronomers as it
36:16 is easy to locate and view with a
36:18 telescope or pair of
36:20 binoculars looking at it is like looking
36:23 into a Celestial Nursery where new stars
36:26 are born
36:28 one of the largest gas and dust clouds
36:30 in our Milky Way galaxy is the Orion
36:33 Nebula it is approximately 2 million
36:36 years old and located about 1,300 light
36:39 years away from
36:41 Earth because the Magnificent nebula has
36:44 an apparent brightness of
36:46 plus4 it is even visible with the human
36:50 eye on the astronomical magnitude scale
36:53 plus 6 is the faintest object that in
36:57 the best lighting conditions is visible
36:59 to the human eye this massive nebula
37:03 which has a diameter of between 30 and
37:06 40 light years could be giving birth to
37:09 a thousand
37:11 stars within the nebula is a young open
37:14 star cluster whose stars are still only
37:17 Loosely connected by gravity after
37:20 having formed together in the gas cloud
37:23 it is sometimes called the Orion Nebula
37:26 star cluster
37:29 an international group of astronomers
37:30 suggested in 2012 that this cluster in
37:33 the Orion Nebula might have a black hole
37:35 at its
37:37 heart through small telescopes you can
37:39 see the four brightest stars in the
37:41 Orion Nebula known as the
37:45 trapezium the Orion Nebula is
37:48 illuminated By the Light of the young
37:50 hot trapesium stars in terms of star
37:54 lives these Stars Are Young having only
37:57 the age of approximately 1 million
38:00 years an infrared picture of the Orion
38:03 Nebula was taken by the James web Space
38:05 Telescope last year it shows an
38:08 explosion of dust stars and clouds in
38:12 red purple and blue against a background
38:15 of dark
38:18 space additionally 540 planetary Mass
38:22 objects with masses ranging from 0.6
38:25 Jupiter masses to Jupiter itself have
38:29 been discovered by James web within the
38:32 nebula among these planetary Mass
38:35 objects the most fascinating are the
38:37 Jupiter Mass binary objects which aren't
38:40 separate objects orbiting in Space by
38:48 [Music]
38:49 themselves our Milky Way galaxy is a
38:53 spiral galaxy a spiral galaxy is a
38:57 Galaxy that looks like a flat rotating
39:00 disc with a bulge in the center and
39:03 spiral arms that extend outward from the
39:07 Bulge while there are many minor arms
39:09 and just two major arms in our spiral
39:12 galaxy astronomers used to believ that
39:15 there were four major
39:17 arms scientists have found that just two
39:20 arms wrapping off the ends of a central
39:22 bar of stars dominate The Milky Way's
39:26 beautiful spiral
39:28 structure these discoveries were made
39:30 possible by NASA's Spitzer Space
39:32 Telescope using infrared imagery the two
39:36 major arms of the Galaxy scutum
39:38 Centaurus and Perseus are visible at the
39:41 tips of a thick Central bar while Norma
39:44 and Sagittarius the two now demoted
39:46 minor arms are situated in between the
39:49 major arms and are less
39:51 distinct although the minor arms are
39:54 mainly made up of gas and areas where
39:56 Stars are forming the major arms have
39:59 the largest densities of both young and
40:02 old
40:04 Stars large telescopes are used by radio
40:07 astronomers to study the Motions of
40:09 those hydrogen clouds that trace the
40:12 arms with a pitch angle of around 9° the
40:16 pereus arm has a spiral extension and
40:19 measures over 60,000 light years in
40:22 length and 1,000 light years in width
40:25 and has the well-known crab nebul
40:27 in addition to double clusters on the
40:30 other hand The scutum Centaurus arm is
40:33 around 55,000 light years in length and
40:37 1,000 light years in
40:39 width our solar system lies between two
40:42 prominent spiral arms the pereus arm and
40:46 The scutum Centaurus
40:48 arm however we are not completely free
40:50 floating in empty space we are situated
40:53 on the edge of the Orion signis arm
40:56 sometimes referred to as the Orion arm
40:59 or local arm which is a small spiral arm
41:04 this spiral arm spans about 10,000 light
41:07 years in length and
41:09 3,500 light years in
41:12 diameter however a 2016 analysis
41:15 indicates that its length May exceed
41:17 20,000 light
41:19 years the Orion arm is named after the
41:22 Orion
41:23 constellation the solar system is
41:25 located in the local bubble on the inner
41:28 Edge inside the Orion arm it is located
41:32 at 26,000 light years from the galactic
41:34 center halfway down the length of the
41:37 Orion arm you might be surprised to hear
41:40 that the sun takes 250 million years to
41:44 complete one rotation around the Milky
41:46 Way this is referred to as a cosmic year
41:50 or Galactic Year thus during its
41:54 lifetime the sun is estimated to have
41:57 completed only 18 to 20 orbits since the
42:00 beginning of
42:02 mankind the solar system orbits the
42:04 Milky Way at a speed of about 220 km
42:08 perss or
42:10 0.73% the speed of light the solar
42:13 system takes around 1,400 years to
42:17 travel one light year at this speed or 8
42:20 days to travel one astronomical unit
42:23 following the ecliptic the solar system
42:26 is traveling toward the zodiacal
42:28 constellation
42:30 Scorpius the last time the solar system
42:32 was in this position in the Milky Way
42:34 There were still dinosaurs on
42:36 earth who knows when it will happen
42:39 again Humanity might be extinct or it
42:43 might have evolved into something else
42:45 entirely our place in the galaxy is
42:48 important because it seems that Galaxies
42:50 have habitable zones just like planetary
42:54 systems because many of the Milky Way's
42:56 Sun
42:58 orbit the Galaxy along paths that take
43:01 them through the deadly spiral arms and
43:04 astounding 95% of them may not be able
43:07 to support habitable
43:10 planets radiation from the crowded stars
43:14 is deadly for any star that goes through
43:17 one of these Stellar
43:19 swarms in order to maintain its
43:21 alignment with the Galaxy's rotation our
43:24 solar system orbits sufficiently far
43:26 from the galactic center to stay in the
43:29 karma region between the spiral
43:33 arms within a large and intricate Galaxy
43:37 the earth and its planetary siblings are
43:39 well situated in a quiet resourcer
43:48 [Music]
43:51 region as we go closer to the center of
43:54 our Milky Way galaxy located roughly
43:57 9,500 light years away from Earth in the
44:00 scotum
44:01 constellation we will reach uy
44:10 scooty it's considered to be one of the
44:13 largest known stars with a radius of
44:16 1.18 billion kilm which is 1,700 times
44:20 larger than the sun's
44:23 radius this would give the star a
44:25 diameter of over eight astronomical
44:29 units that is equivalent to 8 times the
44:32 distance between Earth and the Sun or
44:36 150 million km or 93 million
44:41 miles because of this hyper giant star's
44:44 immense size its outer surface would
44:47 reach well beyond Jupiter's orbit which
44:49 is around five times further from the
44:51 Sun than Earth the gas nebula that is
44:55 ejected from the star stretches 400
44:58 times the distance between Earth and the
45:00 Sun far beyond Pluto's orbit or look at
45:04 it this way more than a million Earths
45:07 could fit inside the Sun but some 5
45:10 billion Suns could fit inside a sphere
45:13 the size of uy
45:15 scooty not surprisingly uy scooty is
45:19 classified as a hyper Giant star which
45:21 is the classification which comes after
45:23 super giant and regular giant although
45:26 it may be the largest due to its size
45:29 but it is not the heaviest or most
45:31 massive star the term mass in massive
45:36 refers to the amount of matter in the
45:39 star the heaviest star is
45:42 r136
45:43 A1 which weighs in at about 300 times
45:47 the mass of the Sun but only about 40
45:50 times the radius of the sun on the other
45:53 hand uy scooty has a size significantly
45:58 larger than the sun although having only
46:01 have a mass between seven and 10 times
46:04 that of the
46:05 sun similarly being so massive doesn't
46:08 mean that UI scoote is that hot either
46:11 in fact its surface is almost half as
46:14 hot as our
46:16 Suns another thing that makes UI scooty
46:19 particularly interesting is the fact
46:20 that it's a variable star over time
46:24 variations in Luminosity can be seen as
46:26 a result of the material's continuous
46:29 fluctuation at and near the surface due
46:33 to the unstable battle between the
46:35 forces of gravity and
46:37 fusion these stars are of special
46:40 interest to astronomers because they can
46:42 shed light on the inner workings of
46:45 stars although uy scooty like many other
46:48 stars is thought to be capable of
46:50 supporting a planetary system it's
46:53 possible that the innermost exoplanets
46:56 have already been swallowed by the host
46:58 Stars
46:59 expansion furthermore uy scooty is so
47:03 faint that it is improbable that we will
47:06 ever be able to witness those exoplanets
47:12 directly as we go to the center of our
47:14 Milky Way galaxy around 26,000 light
47:18 years away we see a Celestial
47:23 Enigma Sagittarius A
47:28 this super massive black hole is an
47:30 incredible Cosmic monster that is beyond
47:34 understanding Sagittarius A is no
47:36 ordinary black hole its estimated mass
47:40 is a staggering 4.3 million times that
47:43 of our sun imagine compressing millions
47:46 of suns into a single point a
47:48 gravitational singularity where space
47:50 and time warp beyond
47:54 recognition this massive monster is
47:56 located at at the heart of the Milky Way
47:59 our spiral
48:01 galaxy a black hole is a region of space
48:04 so densely populated with mass that
48:06 nothing can escape from it not even
48:10 light a black hole is invisible to us
48:13 but telescopes can see the material
48:15 surrounding it black holes surrounding
48:18 matter which can consist of gas and dust
48:22 warms up and releases detectable
48:25 radiation
48:27 in some cases telescopes can observe the
48:29 gravitational influence of a black hole
48:32 on the Motions of nearby individual
48:36 Stars observing it directly is a
48:39 formidable challenge Sagittarius A is
48:42 obscured by a dense layer of dust that
48:45 prevents Optical
48:47 observations however astronomers have
48:50 developed smart strategies to break
48:52 through this Cosmic
48:54 curtain The Event Horizon telescope a
48:58 network of radio telescopes spanning a
49:00 planet made history in April
49:03 2019 when it successfully obtained the
49:06 second ever image of a black hole this
49:09 discovery comes after the EHT
49:12 collaboration released the first picture
49:14 of m87 the black hole at the center of
49:18 the farther off messia 87 Galaxy in
49:22 2019 Sagittarius A was visible in the
49:25 photograph as a dim outline against the
49:28 brilliant background this turbulent
49:30 region known as the accretion disc feeds
49:34 matter to the hungry black hole causing
49:36 occasional x-ray
49:38 flashes despite Sagittarius A being less
49:41 massive and more than a thousand times
49:43 smaller than m87 the two black holes
49:47 look remarkably similar its surrounding
49:50 gas disc which stretches out over a
49:52 distance of 5 to 30 light years can
49:55 reach temperatures of up to 18 million
49:58 de F or 10 million de
50:02 c not only is the super massive black
50:05 hole at the center of our galaxy
50:06 spinning but it's doing so at nearly
50:09 maximum speed consuming everything in
50:12 its path physicists use NASA's Shandra
50:16 x-ray Observatory to study the x-rays
50:19 and radio waves coming from Material
50:21 outflows in order to measure the
50:24 rotating speed of the super massive
50:26 black hole in the Milky Way a black hole
50:30 spin speed is represented by the letter
50:32 a and ranges from 0 to one where one is
50:36 the maximum rotational speed to a
50:39 specific black hole and represents a
50:42 significant portion of the speed of
50:45 light physicist discovered that
50:47 Sagittarius A rotates at a speed of 0.84
50:52 to
50:53 0.96 which is near the upper limit
50:55 determined by the width of a black
50:59 hole the spin of a black hole differs
51:02 from that of other celestial bodies
51:05 black holes are truly regions of
51:07 SpaceTime defined by an outer
51:09 non-physical boundary termed The Event
51:13 Horizon Beyond which no light can escape
51:16 unlike planets stars and asteroids which
51:19 are solid things with physical
51:22 surfaces this implies that as black
51:25 holes spin they literally distort
51:28 SpaceTime itself dragging anything
51:31 inside the ergosphere with them this
51:34 phenomena known as frame dragging or the
51:38 lensing thuring effect which implies
51:40 that knowledge of a black hole spin is
51:43 necessary to comprehend how space acts
51:46 around it Additionally the frame
51:49 dragging around black holes produces
51:51 strange visual effects the path of light
51:55 gets twisted or curved
51:57 as it approaches a revolving black hole
51:59 due to space time's rotation this causes
52:02 a process known as gravitational lensing
52:06 in which the rotating black hole's
52:07 gravitational pull bends the path of
52:11 light frame dragging effects can result
52:14 in the production of light rings and
52:16 even the shadow of a black hole these
52:19 are examples of how light is affected by
52:22 black hole's gravitational
52:24 pull the theoretical top speed of a
52:26 black hole is determined by how it feeds
52:29 on matter and thus how it
52:33 grows as matter falls into a black hole
52:36 it increases the black hole spin but
52:39 there's a limit to how much angular
52:41 momentum it can possess the black holes
52:44 mass is another Factor the gravitational
52:48 attraction of more massive black holes
52:49 is stronger making it harder to spin
52:52 them up this could explain why the
52:55 rapidly feeding super massive black hole
52:57 at the center of Galaxy
52:59 m87 the first black hole ever captured
53:02 on camera is spinning at between
53:06 0.89 and
53:08 0.91 despite having the mass of 6.5
53:12 billion
53:13 Suns while Sagittarius A with its mass
53:17 equivalent to about 4.5 million Suns has
53:21 a spin speed between
53:23 0.84 and 0.96
53:28 but soon something strange happened
53:30 while researching this black hole some
53:33 scientists believe that Sagittarius A
53:37 may not be a black hole after all
53:39 instead it could be an immense
53:41 concentration of Dark Matter imagine a
53:45 dark pool of invisible matter forming
53:48 the basic structure of our
53:50 galaxy Sagittarius A has never been
53:54 directly confirmed despite the fact fact
53:56 that it is widely believed to be a black
53:59 hole to put it simply it is an extremely
54:02 bright radio emitter located at the
54:05 Milky Ways Galactic
54:07 core the astronomy Community encountered
54:10 a challenging problem G2 a Galaxy Cloud
54:15 had moved a bit too close to Sagittarius
54:18 A the G2 gas cloud just kept drifting
54:22 without undergoing any notable changes
54:24 despite the fact the super massive black
54:27 hole should have pulled it and destroyed
54:30 it observing the interaction between the
54:32 Sagittarius A and the G2 gas cloud
54:36 revealed that G2 was not an ordinary gas
54:39 cloud as seen by the lack of effect they
54:43 explain that at least two components had
54:45 to be present to allow the cloud to pass
54:48 through that close to the black hole
54:50 without being
54:52 devoured one is an extended cold and low
54:56 mass gas cloud and the other is a very
54:59 compact segment like a Dusty object that
55:02 dominated the detected emission from G2
55:05 as it passed by astronomers however may
55:09 be more concerned with the possibility
55:11 that Sagitarius a is not actually a
55:14 black hole first scientists created a
55:18 simulation of our galaxy because they
55:20 were intrigued by the idea that the
55:23 Milky Way Center might actually be a
55:25 mass of Dark Matter researchers found
55:29 that despite the galactic Center's
55:31 replacement the Milky Way galaxy still
55:33 exists and operates basically in the
55:36 same manner throughout the
55:39 simulations the behavior of the rotating
55:42 curve in the Milky Way's outer Halo was
55:45 identical to that of nearby s stars or
55:48 those connected to the radio Source
55:51 Sagittarius
55:53 A taking their inquiries a step further
55:56 further they propose that darkos a
55:59 family of particles related to fermans
56:02 May comprise the mass at the center of
56:04 the Milky Way apart from its extreme
56:08 features such as devouring everything
56:10 around it darkos would have the same
56:12 properties as a black hole if they Clump
56:15 together into a huge
56:18 mass Sagittarius A is mostly dormant and
56:23 only occasionally absorbs gas or dust
56:26 but nonetheless has an estimated Mass
56:29 Millions times that of our sun although
56:32 there are still a lot of unanswered
56:34 questions concerning the super massive
56:36 black hole future observations from The
56:39 Event Horizon telescope should shed
56:42 light on these
56:44 riddles Stellar mass and intermediate
56:47 Mass black holes form when massive stars
56:51 cease nuclear fusion and can no longer
56:54 support themselves against complete
56:55 gravitation ational collapse the
56:58 mechanism that forms super massive black
57:00 holes like Sagittarius A is unclear
57:03 because there are no stars large enough
57:05 to directly collapse into a black hole
57:08 of this
57:09 size there are two possible explanations
57:13 either smaller black holes merge in
57:15 order to form larger black holes or
57:18 smaller black holes grow enormously
57:20 large by consuming gas and dust from
57:23 their surrounding
57:26 Sagittarius A remains an astronomical
57:29 Marvel a cosmic mystery at the heart of
57:32 the Milky
57:34 Way as our understanding deepens we
57:37 continue to unravel our galaxy
57:48 secrets in
57:50 197 American astronomer harlo shapley
57:53 provided the first reliable measurement
57:55 of the Galaxy size he determined the
57:58 size by first determining the globular
58:00 cluster's spatial
58:02 distribution as had been previously
58:05 believed chapley discovered that the
58:07 Galaxy is enormous with the Sun closer
58:10 to its periphery than its Center rather
58:13 than a relatively compact
58:15 system assuming that the globular
58:17 clusters surround the Galaxy he
58:20 calculated that the galaxy has a
58:22 diameter of roughly 100,000 light years
58:26 or 600,000 trillion
58:28 miles the sun is located approximately
58:32 30,000 light years from the Galaxy's
58:35 Center his values have held up
58:38 remarkably well over the years the Milky
58:40 Way Stellar disc is roughly the size
58:43 predicted by shapley's
58:45 model dark matter or invisible matter
58:49 may fill an even larger volume than
58:51 expected while neutral hydrogen is
58:54 somewhat more widely distributed
58:57 according to recent calculations a dark
59:00 matter area that includes a few visible
59:02 stars might have a diameter of about 2
59:05 million light
59:07 years in addition to having multiple
59:09 satellite galaxies the Milky Way is a
59:12 member of the local group of
59:14 galaxies which is a subcluster of the
59:17 Virgo
59:19 supercluster which is itself a component
59:22 of the Lena supercluster
59:25 [Music]
59:30 there are at least 100 to 400 billion
59:32 stars in our galaxy and at least that
59:34 number of
59:36 planets the Milky Way and everything
59:38 else in space are in
59:40 motion the radiation from The Big Bang
59:42 known as The Cosmic microwave background
59:45 is used as a reference point for
59:48 calculating the speed of objects in
59:51 Space the Milky Way galaxy is thought to
59:54 be traveling at a speed of rough roughly
59:56 600 km/s or 372
60:00 m/s inside the local group of
60:04 galaxies since the oldest stars in the
60:06 Milky Way are almost as old as the
60:08 universe they most likely formed shortly
60:11 after the big Bang's Dark
60:14 [Music]
60:17 Ages the galactic nucleus is the site of
60:20 a wide range of activity apparently
60:23 powered by the black hole the region
60:26 emits X-rays and infrared light and it
60:29 is possible to see fast moving gas
60:31 clouds
60:32 there data clearly show that matter
60:35 including some gas from the Z direction
60:38 that is perpendicular to the galactic
60:40 plane is being drawn into the black hole
60:42 from outside the nuclear
60:45 Zone as the gas nears the black hole the
60:48 central objects strong gravitational
60:51 force squeezes the gas into a rapidly
60:54 rotating disc which extends outward
60:57 about 5 to 30 light years from the black
61:01 hole surrounding the nucleus is an
61:04 extended bulge of stars that is nearly
61:07 spherical in shape and that consists
61:10 primarily of population two stars though
61:13 they are comparatively rich in heavy
61:16 elements a star's metallicity or the
61:19 amount of elements heavier than helium
61:21 in its composition divides Stars into
61:24 three primary population
61:27 groups population three are the oldest
61:30 and population one stars are youngest
61:33 like our
61:35 son the disc portion of the Galaxy
61:38 contains the population one Stars their
61:41 ages range from 0 to 10 billion
61:46 years the spiral arms include the
61:48 younger ones the orbits of population
61:51 one stars are well organized with
61:53 roughly circular paths in the Galactic
61:56 discs
61:59 midplane Young Star clusters made of
62:02 population one stars are called open
62:04 clusters because the stars are Loosely
62:07 bound together in contrast to the old
62:09 concentrated globular clusters compared
62:12 to population 2 Stars population one
62:15 stars have a higher abundance of
62:17 elements heavier than
62:19 helium astronomers frequently refer to
62:22 elements heavier than helium as
62:24 Metals the oldest population one stars
62:27 have somewhat eccentric orbits that can
62:30 carry them up to 3,000 light years from
62:32 the dis plane and they have a metal
62:35 abundance 0. one times that of the
62:38 Sun the population two stars inhabit the
62:42 spheroidal component the Stellar Halo
62:45 and
62:46 bulge they have masses of less than or
62:49 equal to 0.8 solar masses because they
62:52 are old their ages range from from 10 to
62:56 13 billion years their orbits are much
63:01 more randomly oriented than the
63:03 population one orbits and are highly
63:05 elliptical as a unit the spheroidal
63:08 component has little overall
63:11 rotation population two stars make up
63:15 globular clusters globular clusters were
63:18 used to find the center of the Galaxy
63:20 because they swarm around the center
63:22 like bees around a hive
63:26 on the other hand population three stars
63:29 are those that have not been directly
63:32 observed they are believed to have
63:34 virtually no heavy elements at all these
63:37 stars are thought to be the first ones
63:39 that formed in the primordial Universe
63:42 shortly after the big bang they were
63:45 extremely massive and hot and they
63:48 burned their fuel very rapidly turning
63:51 hydrogen and helium into heavier
63:54 elements when when they die they explode
63:58 as Supernova scattering some of these
64:01 elements into the surrounding
64:04 space these Stars probably created the
64:07 first heavy elements that became part of
64:10 later stars and to have played a key
64:13 role in the formation of the first
64:16 galaxies numerous globular clusters of
64:19 related stars are mixed in with the
64:22 Stars and both the stars and the
64:24 Clusters orbit the the nucleus almost
64:28 radially our galaxy is surrounded by a
64:31 huge Hot Gas Halo that is several
64:33 hundreds of thousands of light years in
64:36 diameter a Halo is a spherical cloud of
64:39 stars surrounding a Galaxy the mass of
64:43 the Halo is thought to be roughly equal
64:45 to the total mass of all the Milky Ways
64:50 Stars astronomers have proposed that the
64:53 Milky Ways Halo is composed
64:56 of two populations of
64:58 stars the parano observatory's findings
65:01 indicate that the stars in the inner
65:03 Halo are
65:05 11.5 billion years
65:08 old the outer Halo is thought to be made
65:10 up of the Stellar components of smaller
65:13 Galactic
65:14 systems the stars in the Halo are older
65:17 and have lower metal content in them
65:20 than the majority of the stars in the
65:22 Milky Way's disc the Halo also contains
65:26 gas and dark
65:29 matter the Halo is evidence of the two
65:31 galaxies that collided billions of years
65:34 ago and reinforces the idea that the
65:36 Milky Way has a dynamic origin
65:40 story in the Milky Ways Stella Halo
65:44 astronomers have also found more than
65:47 200 far-off variable Stars referred to
65:50 as Lyra Stars these Stars serve as
65:53 important standard candles that are used
65:56 to measure astronomical distances and
65:58 are often found in globular clusters the
66:01 farthest star from Earth is about a
66:04 million light years away which is nearly
66:06 half the distance to
66:09 Andromeda about 90% of the matter in our
66:12 galaxy is dark matter or matter that is
66:14 invisible to the human
66:17 eye stars make up the remaining 10 to
66:20 15% of the visible stuff in the Milky
66:24 Way which is composed osed primarily of
66:26 gas and
66:28 dust simulations of the Milky Way's
66:31 rotation have shown that this massive
66:34 amount of Dark Matter produces an
66:37 invisible
66:38 Halo if the Dark Matter did not exist
66:41 then the Stars within the Milky Way
66:43 would orbit much slower than has been
66:46 observed the Milky Way's Dusty ring can
66:50 be observed in the night sky on a clear
66:53 night as we are located at approximately
66:56 26,000 light years away from the center
66:59 of the Milky Way we are unable to
67:02 capture images of the disc any depiction
67:05 of our galaxy that you have ever seen is
67:08 either an artist portrayal of it or a
67:11 separate spiral
67:13 galaxy we don't have a picture of the
67:15 Milky Way as a whole since we can only
67:17 capture images of it from within the
67:20 Galaxy so why do we believe that it is a
67:24 barred spiral galaxy
67:25 [Music]
67:27 there are several Clues the first clue
67:29 to the shape of the Milky Way comes from
67:31 the bright band of stars that stretches
67:34 across the
67:36 sky in locations with dark night skies
67:39 this band of stars can be viewed with
67:41 the naked
67:43 eye that band comes from seeing the disc
67:46 of stars that forms the Milky Way from
67:49 inside the dis and tells us that our
67:52 galaxy is basically flat
67:55 many telescopes both on Earth and in
67:58 space have captured photographs of the
68:01 Milky Way disc by capturing a sequence
68:04 of images in different directions which
68:07 is similar to creating a panoramic photo
68:10 with your phone or
68:11 camera the concentration of stars in a
68:14 band adds to the evidence that the Milky
68:17 Way is a spiral
68:20 galaxy if we lived in an elliptical
68:22 galaxy we would see the stars of our
68:24 galaxy spread out all around the sky not
68:28 in a single
68:30 [Music]
68:37 band the Milky Way galaxy was believed
68:40 to be only a few thousand light years
68:42 large until around a century ago and
68:45 most people believed it to be the whole
68:47 universe although other galaxies had
68:49 been found it was believed that they
68:52 were only tiny objects inside our galaxy
68:56 French astronomer Charles Messier
68:59 discovered the first galaxies in the
69:00 17th century although he had no idea
69:03 what they were at that time as a skilled
69:06 Comet Observer Messier saw several
69:09 additional fuzzy objects in the sky that
69:12 he was certain were not
69:14 comets fearing that other Comet Hunters
69:17 would be misidentified as well he put
69:19 together a list to help them out on
69:23 messier's list 110 star clusters and
69:26 spiral nebula were detected the objects
69:29 are denoted by M for Messier followed by
69:31 a number for example
69:35 M51 however it took astronomers nearly
69:38 300 years to figure out the fuzzy spiral
69:41 nebuli some claimed that these nebuli
69:44 were Island universes which are objects
69:47 that are similar to the Milky Way galaxy
69:49 but exist outside of it others disagreed
69:53 and thought that these spiral objects
69:55 were actually Milky Way gas
69:58 clouds the dispute continued until the
70:01 1920s when American astronomer Edwin
70:03 Hubble measured the precise distance to
70:06 a spiral nebula Hubble discovered that
70:10 one of the objects he was seeing was
70:12 actually a sephi variable star in
70:16 1923 while studying the Andromeda nebula
70:19 which is now known as the Andromeda
70:22 galaxy first identified in the early
70:25 1900s by American astronomer henrieta
70:28 lit cides a Stars whose brightness
70:31 changes periodically over time levit
70:35 discovered a connection between a seid's
70:37 Luminosity or brightness and its period
70:40 that is now known as the period
70:42 Luminosity the pl
70:45 relationship the pl relationship can be
70:47 used to calculate the actual brightness
70:50 of a seide by calculating its period
70:53 which is obtained by measuring changes
70:55 in brightness over a period of days or
70:58 weeks Hubble established that the seide
71:01 he was studying in M31 was located
71:04 outside of our own Galaxy by calculating
71:07 its distance using the pl
71:11 ratio this put an end to the controversy
71:14 surrounding the spiral nebuli and proved
71:17 that they were in fact far off galaxies
71:20 similar to the Milky
71:23 Way Hubble continued his study of Galaxy
71:26 distances using seides as his measuring
71:29 tool before publishing his results in
71:33 1929 in his work Hubble created a graph
71:37 showing the distances from CI variables
71:39 and the velocities of galaxies which is
71:42 obtained from estimating the red shift
71:44 of these galaxies Spectra the majority
71:47 of galaxies are moving away from us or
71:50 receding according to this graph and
71:52 their rate of motion the recessional
71:54 velocity is inversely correlated with
71:57 their distance from us distant galaxies
72:01 recede more quickly than nearer ones
72:04 This was later known as Hubble's Law
72:07 Hubble's initial estimates for the
72:09 recessional velocity of galaxies was
72:11 very high because at the time no one
72:14 knew that there were actually several
72:16 different types of seide variables with
72:19 slightly different period Luminosity
72:22 relationships but as astronomy has
72:24 advanced recently ly the value of the
72:26 graph's slope known as Hubble's Constant
72:29 has been reduced and the results are now
72:32 converging toward an accepted value of
72:34 about 65
72:36 km/s or that galaxies recede by an
72:39 additional 65 km/s for every megap Parc
72:44 they are away from us there are
72:47 trillions of galaxies in the universe
72:49 and up to a few hundred billion stars
72:52 can be found in each Galaxy the same way
72:55 that one studies atoms to understand the
72:57 qualities of a material one must study
73:00 the building blocks of the universe to
73:02 comprehend
73:04 it understanding the formation and
73:07 evolution of galaxies is essential for
73:10 our understanding of the
73:13 universe although the study of Galaxy
73:15 formation dates back around 50 years to
73:18 the foundational work of Egan Linden
73:21 Bell and
73:22 Sandage we still do not have a
73:24 comprehens ensive understanding of how
73:26 galaxies form and
73:28 evolve many details still need to be
73:32 explored in addition to providing us
73:34 with valuable answers to the questions
73:36 like where do we come from and where are
73:39 we
73:41 going observation of galaxies other than
73:43 our own also enables us to draw several
73:47 conclusions about the evolution of the
73:50 universe but the only Galaxy we have
73:53 access to a vast amount of data on its
73:56 stars is our own the other galaxies are
74:00 just too far away for us to observe Star
74:03 by
74:05 star before we continue one might wonder
74:08 if knowledge of the Milky Way's
74:10 development provides any insight into
74:13 knowledge of other galaxies the answer
74:15 is
74:17 yes approximately 50% of stars in the
74:21 modern Universe reside in Milky Way like
74:24 galaxies
74:26 to put it another way the Milky Way is a
74:28 fair representation of a typical galaxy
74:31 in the
74:32 universe our knowledge of the Milky
74:35 Way's development will provide a strong
74:37 foundation for our understanding of
74:40 other
74:42 [Music]
74:48 galaxies soon after the big bang which
74:51 occurred
74:54 13.61% the Milky Way began as one or
74:57 more small over densities in the
75:00 universe's Mass
75:02 distribution some of these over
75:04 densities were the seeds of globular
75:07 clusters in which the oldest remaining
75:09 stars in what is now the Milky Way
75:13 formed it's possible that about half of
75:16 the material in the Milky Way originated
75:19 in other far off
75:21 galaxies these star groups and
75:23 individual stars now make up the Milky
75:25 Way's Stellar Halo the Milky Ways Mass
75:29 reached a point where it began to rotate
75:32 relatively quickly only billions of
75:35 years after the first stars were born
75:38 because of the conservation of angular
75:40 momentum this caused the gaseous
75:42 interstellar medium to compress into a
75:45 disc from a roughly spheroidal shape
75:49 therefore later generations of stars
75:51 formed in this spiral disc
75:55 throughout its history the Milky Way has
75:57 consumed many galaxies to get to its
76:00 current size and form in the last 12
76:03 billion years the Milky Way has
76:05 swallowed up more than a dozen
76:08 galaxies according to cosmological
76:10 simulations it merged with a
76:12 particularly massive galaxy known as the
76:15 Kraken approximately 11 billion years
76:19 ago our galaxy is currently consuming
76:22 the Canis Major dwarf Galaxy by by
76:25 adding the smaller Galaxy stars to its
76:27 own
76:29 spiral at present the Milky Way is
76:31 traveling at a speed of
76:33 250,000 mph in the direction of the
76:38 Andromeda
76:39 galaxy it is expected that the two
76:42 galaxies will collide in roughly
76:45 4.5 billion
76:47 years the Milky Way and Andromeda are
76:50 the two largest galaxies in the local
76:53 group they will merge because before
76:55 dark energy took over they became
76:58 gravitationally bound to one another the
77:00 merger is expected to change the night
77:03 sky over Earth the Milky Way is orbiting
77:07 a point in space that is roughly halfway
77:10 between it and the Andromeda
77:13 galaxy although it's difficult to
77:15 believe experts think that our solar
77:17 system probably will survive such a
77:20 terrible
77:21 event since galaxies are primarily made
77:24 of empty space this Collision will not
77:27 have a significant impact on our solar
77:30 system despite having 100 billion stars
77:34 each our galaxy and the Andromeda galaxy
77:37 are very far
77:39 apart currently Andromeda is located 2.5
77:44 million light years away from
77:47 Earth similar to how a ball in the air
77:50 accelerates faster as it falls toward
77:52 Earth Andromeda will be drawn closer and
77:55 faster by the Milky Way's increasing
77:57 gravitational pull as it gets closer in
78:01 Just 4 billion years the Milky Way and
78:04 Andromeda will have tugged and ripped at
78:07 one another's throats all that's left
78:10 will be the spectral framework of two
78:12 separate galaxies in the
78:15 past the Carnage will go on for as long
78:18 as time does not stop until the central
78:21 super massive black holes in both
78:23 galaxies are near enough to one another
78:25 to collide and
78:28 join by that point the Milky Way and
78:31 Andromeda galaxies the two separate
78:35 spiral galaxies will be no more our
78:38 solar system will have a new home in an
78:41 entirely different class of Galaxy
78:43 called an elliptical
78:50 galaxy what about life on Earth then
78:55 will life on Earth continue after the
78:59 merger well in roughly 7.5 billion years
79:02 the sun will grow larger and swallow the
79:05 Earth turning it into a red giant this
79:08 will happen ultimately in a timeline of
79:11 about 4 billion
79:12 years as solar radiation reaching the
79:15 Earth increases Earth's surface
79:17 temperature will
79:19 increase we might experience a runaway
79:22 greenhouse effect much like what's
79:24 happening right right now on
79:25 Venus thus there's a good chance that
79:28 life on Earth won't exist after the
79:32 merger however perhaps by then some
79:35 people on Earth will have developed
79:36 space travel abilities it's possible
79:39 that we will have abandoned Earth and
79:42 our solar
79:43 system the view of Andromeda colliding
79:46 with the Milky Way might still be
79:48 available to us although from a slightly
79:51 different angle
79:55 as we gaze up let's realize how short
79:59 our life
80:00 is we are Stardust seeing a cosmic
80:05 tale for whatever reason we are here now
80:09 sitting and wondering about the
80:12 universe we the very Children of the
80:15 universe born from ordinary chemicals
80:17 over billions of years now gaze
80:20 wondrously into the endless black abyss
80:23 to think about it
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