Milky Way stars that are high and low in metallicity have been mapped by the ESA Gaia mission. [Gaia spacecraft: Mapping the Milky Way like never before.
Credit: ESA/Gaia/DPAC
Credit: ESA/Gaia/DPAC
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TechTranscript
00:00 [Music]
00:13 Gaia's main objective is to determine the positions, motions and distances of billions of stars.
00:20 When the images of the stars from Gaia's telescopes move across the focal plane,
00:25 their positions at a given time are determined by the light-sensitive astrometric CCDs.
00:31 [Music]
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,
00:55 allowing us to determine the speed of the stars along the line of sight and their chemical composition.
01:01 [Music]
01:05 This animation presents some of these stellar spectra,
01:08 where the brightness of the stars 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 atmosphere.
01:19 Most of the ordinary matter in the Universe consists of the lightest elements,
01:24 hydrogen or helium, created during the Big Bang.
01:27 For all heavier elements, such as calcium and iron, astronomers use the word "metals".
01:33 Most of these "metals" were created by nuclear fusion in stars
01:38 and given back to the interstellar 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.
01:48 [Music]
01:51 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.
02:02 The stars shown here are those for which the chemical compositions could be determined with the RVS spectrograph.
02:10 Older stars should contain only a small amount of metals,
02:14 while stars born later should have a higher metallicity.
02:18 We now travel thousands of light-years towards the centre of our Milky Way
02:23 and observe stars with very different amounts of metals in their atmospheres.
02:27 [Music]
02:36 Now we fly out of the plane of our galaxy
02:39 [Music]
02:42 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 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,
03:15 which can be detected 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 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,
03:41 we can infer the rate at which the stars were born,
03:44 the arrival of gas from the intergalactic regions,
03:47 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,
03:57 and therefore about four billion years younger than our Sun.
04:01 They are located along curves that reveal the spiral arms of the Milky Way where these 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.
04:29 This allows us to visualise the motion of the stars as measured by Gaia.
04:34 This short sequence corresponds to five million years.
04:38 We see that the stars move together, illustrating the stellar motions in the disk of our Milky Way.
04:44 Let us now move to the plane of our Milky Way and see our galaxy edge on.
04:55 First, we look again at our full sample of stars for which the chemical compositions could be determined by Gaia Data Release 3.
05:03 In the following, we will split this sample into the same groups as before.
05:08 Now we show the sample of giant stars edge on.
05:12 These luminous stars allow us to determine the chemical profile of the Milky Way disk,
05:17 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, like the chemical enrichment.
05:29 In addition, in the inner regions, the stars near the galactic plane are more enriched in metals than the older stars,
05:36 at higher distances above and below the plane.
05:39 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 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.
06:01 Again, we show how these stars will move during the next five million years.
06:08 We can see the disk rotation, with the stars approaching in our direction.
06:14 Up to now, we have shown the overall global enrichment in chemical species in the atmospheres of the stars.
06:22 However, we have also determined individual abundances of chemical elements.
06:28 As an example, we colour-code here the amount of calcium in the young stars,
06:33 an element which is, for instance, important for the stability of our bones.
06:39 [Music]
06:46 Finally, we show a group of stars that has no strong concentration towards the galactic plane.
06:52 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 Way about 8 to 11 billion years ago.
07:12 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.
07:23 [Music]
07:31 [Music]
07:41 [BLANK_AUDIO]