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Gaia Mission Measures Metals In Milky Way Stars
Space.com
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25/07/2024
Milky Way stars that are high and low in metallicity have been mapped by the ESA Gaia mission.
Credit: ESA/Gaia/DPAC
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Tech
Transcript
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00:00
Gaia's main objective is to determine the positions, motions and distances of billions
00:19
of stars.
00:20
When the images of the stars from Gaia's telescopes move across the focal plane, their
00:25
positions at a given time are determined by the light-sensitive astrometric CCDs.
00:36
Subsequently, the light from the star passes through prisms, producing low-resolution spectra,
00:42
helping us to determine, for example, the temperature of the stars.
00:46
Finally, the diffraction grating and carefully crafted lenses in the radial velocity spectrograph
00:52
disperse the light into high-resolution spectra, allowing us to determine the speed of the
00:56
stars along the line of sight and their chemical composition.
01:05
This animation presents some of these stellar spectra where the brightness of the stars
01:10
is shown as a function of wavelength.
01:12
The variations are due to the light absorption from atoms and molecules present in the stellar
01:17
atmosphere.
01:20
Most of the ordinary matter in the universe consists of the lightest elements, hydrogen
01:25
or helium, created during the Big Bang.
01:28
For all heavier elements, such as calcium and iron, astronomers use the word metals.
01:34
Most of these metals were created by nuclear fusion in stars and given back to the interstellar
01:39
medium, for example, by stellar winds and supernova explosions.
01:43
In this way, our Milky Way is enriched in metals over the course of time.
01:52
Here we are using the metal abundances derived from the RVS to colour the stars.
01:57
Blue represents a low metallicity, red a high one, green lies in between.
02:04
The stars shown here are those for which the chemical compositions could be determined
02:08
with the RVS spectrograph.
02:11
Older stars should contain only a small amount of metals, while stars born later should have
02:16
a higher metallicity.
02:18
We now travel thousands of light years towards the centre of our Milky Way and observe stars
02:24
with very different amounts of metals in their atmospheres.
02:36
Now we fly out of the plane of our galaxy and look down on the Milky Way from above.
02:46
In order to see all of the stars of our sample, we enhance their brightness and move closer
02:51
to them.
02:54
The distribution of metals shown here results from the mixture of stars of different luminosities.
03:02
Gaia can detect dwarf stars with very low luminosities only if they are very close to us.
03:10
Therefore we now select only the very luminous giant stars in our sample, which can be detected
03:16
by Gaia even at a distance of several thousand light years.
03:20
We see that the enrichment in metals decreases as we move from the galactic centre to the
03:25
outer galactic regions.
03:27
This informs us about the chemical composition of the gas from which these stars were formed
03:33
over more than 12 billion years of galactic history.
03:37
Therefore, and thanks to the high level of detail of these Gaia observations, we can
03:41
infer the rate at which the stars were born, the arrival of gas from the intergalactic
03:46
regions and the migration of stars inside the disk.
03:51
The next sample consists of very young stars, only a few hundred million years old, and
03:57
therefore about 4 billion years younger than our Sun.
04:01
They are located along curves that reveal the spiral arms of the Milky Way where these
04:07
stars were formed.
04:08
The Sun is in a region outside the spiral arms.
04:11
We see again the decrease in the metal enrichment as we look further outwards in our galaxy.
04:16
This is the largest sample of young stars for which we have a detailed chemical description,
04:21
thanks to Gaia Data Release 3.
04:23
Because there are fewer of the young stars, we can show more of them individually.
04:30
This allows us to visualise the motion of the stars as measured by Gaia.
04:35
This short sequence corresponds to 5 million years.
04:39
We see that the stars move together, illustrating the stellar motions in the disk of our Milky
04:44
Way.
04:48
Let us now move to the plane of our Milky Way and see our galaxy edge-on.
04:56
First we look again at our full sample of stars for which the chemical compositions
05:00
could be determined by Gaia Data Release 3.
05:04
In the following we will split this sample into the same groups as before.
05:09
Now we show the sample of giant stars edge-on.
05:13
These luminous stars allow us to determine the chemical profile of the Milky Way disk,
05:18
including its older stellar populations, far from the galactic plane.
05:21
As we move outwards from the galactic centre, the disk density and apparent thickness decreases
05:27
like the chemical enrichment.
05:30
In addition, in the inner regions, the stars near the galactic plane are more enriched
05:34
in metals than the older stars, at higher distances above and below the plane.
05:41
This is the sample of young stars, shown from the side.
05:45
The stars in the spiral arms are located in the so-called thin disk, which has gas and
05:51
ongoing star formation and to which our Sun belongs.
05:55
This thin disk profile becomes thicker as we move outwards from the galactic centre.
06:04
Again we show how these stars will move during the next 5 million years.
06:08
We can see the disk rotation, with the stars approaching in our direction.
06:16
Up to now we have shown the overall global enrichment in chemical species in the atmospheres
06:21
of the stars.
06:23
However, we have also determined individual abundances of chemical elements.
06:29
As an example, we colour-code here the amount of calcium in the young stars, an element
06:34
which is, for instance, important for the stability of our bones.
06:47
Finally we show a group of stars that has no strong concentration towards the galactic
06:52
plane.
06:53
Almost all of them are very poor in metals, and therefore shown as blue in this video.
06:58
The stars were identified by their peculiar motion and chemical composition.
07:03
They are the remains of a dwarf galaxy, called Gaia Enceladus, that merged with our Milky
07:08
Way about 8 to 11 billion years ago.
07:13
These stars illustrate that the galaxy in which we live is an ever-changing system,
07:18
formed thanks to the assembly of stars and gas of different origins.
07:33
Transcription by ESO. Translation by —
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