Saturday , February 27 2021

How Gaia will map the galaxy to one star at a time – Brinkwire



The astronomical community is preparing for the great: a spectacular, 3D map of the entire Milky Way.

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Astronomy is often called the oldest branch of science. From ancient times, people watched the sky, cataloged their inhabitants, marked new arrivals, and displayed permanent stars and the attic of the planet.

For many millennia, great progress has been made in astronomy, but there are some surprisingly basic questions: where exactly are the stars? Where is the Big Scheme of the Earth? What is the shape and structure of our home galaxy?

We have come a long time from thinking about stars as a two-dimensional projection in the sky, but the measurement of the star distance remains quite complicated. And even tracking the starry motion in the sky in two dimensions is difficult without annual data.

In 1989, the European Space Agency (ESA) began to measure the position of 2.5 million stars of the Hipparcos satellite, a catalog that was not fully published until 2000. In 2013, the ESA launched Gaia, which will return even higher accurate data to more than a billion stars. Gaia was a Greek goddess who was considered a kind of Mother Earth. The ESA mission originally referred to the "Global Astrometric Interferometer for Astrophysics". Although many parameters have changed, the ESA has retained the name for the continuity of the mission.

Gaia will not complete its mission by 2019, and a final data analysis will not be available only years later. But in September 2015, the Gaia science team released the first round of data from 14 months of observation and welcomed scientists around the world to jump. The results are already changing the perspective of the astronomers of our galaxy.

With numbers

Gaia's mission statement is supposed to "map out billions of stars," but even this bold promise does not have the real ability of the space observatory. Gaia, which circles about 932,000 miles (1.5 million kilometers) and a map of the sky, carries three instruments. His astrometric instrument shows the positions and movements of stars with precise precision, observing how they appear to be moving through the course of Gaia's five-year mission. Its photometric camera measures the brightness of the stars in red and blue wavelengths, thus obtaining data on its temperatures and compositions. Finally, the spectrometer measures the Doppler shift of certain chemical signatures to reveal whether the stars are moving towards or away from the Earth. (For a detailed overview of the plan and mission of Gaia, see AstronomyThe story of December 2014, "How Gaia will map a billion stars.")

Over time, Gaia's goal is to make the distance of 100 million stars better than 10 percent accuracy. For 10 million objects, the error rate will be less than 1 percent. It will measure positions and movements of more than a billion stars all over the sky, up to twelve sizes, with an accuracy of a few millionth of a hole, by crushing previous research.

But for the first release of data, Gaia needed some help. Gaia measures the motion of stars to determine their distance. Since the first year of data, it is impossible to expel the movement of stars from the telescopic motion, as it follows Earth's orbit around the Sun. But the Hipparcos satellite has already done this work once for millions of target stars of the Gaia star. The Hipparcos catalog knows where those stars were 20 years ago, and Gaia knows where they are now, even more precisely. This extended time period was what Gaia needed.

Thus, the Gaia group combined the ultimate Hipparcos catalog called Hipparcos-Tycho 2, with Gaia data so far. The astronomical solution of Tycho-Gaia (TGAS) is the first step on an updated map, which will eventually include a stellar position in 3-D and its motion, more precisely than ever before. For now, it contains 2 million stars, measured twice as precisely as Hipparcos itself. At the end of Gaia's mission, the data of Hipparcos will be replaced by more detailed Gaia measurements. But while Hipparcos – and some other surprising sources – give Gaiji a helping hand.

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Star Scale

One of Gaia's great tasks is the calibration of the cosmic distance, which requires some star tools. Astronomers use two types of variable stars, called the Cepheid variables and the RR Lyrae stars, which illuminate and fade at regular intervals. The time they need to enlighten and glitter the scales in an orderly way with how they are truly bright. So, if the two Cepheids have the same period, but it seems that one is bad, then this star must be far away. Astronomers can determine their distance by observing time and light.

Although this system is supposed to work, astronomers need to understand the relationship between period and light well. To calibrate it, they need to know the distance to some of these variable stars. Gaia will measure nearby stars using parallax or the apparent change in the position of the star due to the Earth motion around the Sun. The summer star will appear in front of a different star in the background when Earth (and Gaia circling in a stable point for our planet) on one side of the solar system, as in the winter when the earth changed its position with the 2 astronomical unit (the astronomical unit average distance between the Earth and the Sun).

You can simulate this technique simply by holding your finger in front of your face and looking at it only with your left eye and then your right. Your finger appears to change the position according to the objects in the background. So, in astronomy, nearby stars have a greater apparent change of position than a long star, and this change in the apparent position reveals their real distance from the Earth. This independent distance measurement allows astronomers to calibrate the relationship between the period and the brightness of variable stars.

At the end of the Gaia mission, the correlation must be sharp. Accurate measurement of the distance to the nearby variable stars and the aggravation of the period between the period and the illumination will allow astronomers to extend this scale to the more distant stars, resulting in accurate distances to longer variable stars.

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Getting started

What can astronomers do with partial Gaia research? A lot.

One of Gaia's goals is to provide an updated map of the Milky Way. Approximately 400 million Gaia's finds are new to human catalogs, as it solves objects that were previously treated as individual light points in several stars.

Using TGAS, astronomers can better understand how the stars move, thereby illustrating the structure of our galaxy – and some of their neighbors.

An early surprise, provided by Gaia, was a stunning image of the Milky Way. "I asked for this picture, but it was much better than I expected," says Anthony Brown, a member of the Gaia's science team. Brown is also chairman of the Gaia Consortium for Data Processing and Analysis, which combines Gaia's data on intelligible scientific data. The clarity of the image and the number of goals also indicate that the Milky Way is larger than previous estimates, although exact numbers are likely to wait until later releases of data.

In particular, the neighboring Magellanic Cloud is also larger than expected. Researchers can explore this mined galaxy from the outside, and Gaia has shown that several stars, as expected, are related to their motion in the universe. Gisella Clementini, a member of the Gaia Group in Italy, explains: "We have been detailed in detail with much more powerful instruments than we had before … Even if they are around the corner because they are close, you can find things."

One of the Gaia test trials was to produce a color diagram; who plan the colors of stars in comparison with their brightness and where they fall into the diagram, tell astronomers about their species and evolutionary stages. Most often these diagrams are generated from astrophysical star models, but not with actual data. But Gaia's vision and measurements have already provided enough data to create a rough diagram, and his entire catalog should allow researchers to build an obviously clear diagram based exclusively on data that would allow theoreticians to develop their models.

Gaia is also identified in the Milky Way 1.394 variable stars that change light at certain times. Of these, 386 were not observed in previous studies. These variable stars are the first wave of targets that Gaia helps with one of its other primary goals.

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Surprise events

Even before the first release of data, Gaia shared some stellar surprises with a larger community. The data processing team marked interesting objects that would earn quicker searches, such as outbreaks of stars, black holes or supernova explosions. Such objects could be stopped until formal data was issued, and the investigators would be robbed of the ability to monitor other telescopes.

In September 2014, Gaia announced a supernova named Gaia14aaa. Gaia saw the host galaxies rise dramatically between the months and months, and astronomers quickly followed two earth telescopes. By studying the spectrum or light signature of the galaxy, it was found that the bright light represented the type of Ia supernova when the white dwarf with an old companion tilted into the explosion itself.

Another surprising source, called Gaia14aae, expanded into Gaia's vision in August. Astronomers eventually found that this is a cataclysmic variable or a system of two stars that can be calibrated. An uneven material spin can cause energy outbursts of light. Both professional as well as amateur astronomers followed and discovered that the stars had no signature of hydrogen, which represents most of the stars in the universe. Both stars are old and have consumed all of their useful hydrogen and put them in a rare class of cataclysmic variables called the AM Canum Venaticorum stars, named for the first system of this type.

With Gaia's view of all the air, the research will continue to appear in transient sources – from a few to 10 a day filtered from around a million potential objects that jumped from the first passage through the data – which the general astronomical community can display.

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Freedom of information

The issue of the Hipparcos catalog required ESA flights that await the entire study to be complete and fully analyzed. With Gaia, they return the door early. While the research is not yet complete, the scientific team believes that at the beginning of this process, there is a great interest in placing it in the scientific community.

David Hogg, a researcher at the University of New York, and an advocate of open access to science, could not be more enthusiastic. He has organized "hack days" at astronomical conferences for several years and even expanded them to "hack weeks." In line with more traditional computer programming, hack days – which are more about building things fast rather than any kind of cyberattack – are based on the idea that if you're going to direct enough people into the work space, brilliant ideas and solid results will follow.

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Only a month after the first release of data, Hogg and some colleagues in New York had Gaia "sprint". "It's obvious to me that a lot of science will come from the sprint," says Hogg. Multiple documents are already available online or circulated through their own and other mailboxes for researchers when they collect comments before publication. All in his opinion, they represent science. Among them were Brown and Alcione Mora, a member of the Gaia Group. But here they were outside associates.

Vasily Belokurov from the University of Cambridge pulled out a completely unexpected sub-catalog. In the future, Gaia will produce a complete catalog of variable stars that act as invaluable marks at cosmic distance. So far, this collection is small and is limited to a short list, which Gaia listed early in his mission, but Belokurov says that a much larger catalog is hidden in a simple way.

With photometric uncertainties, Gaia used evidence that stars with greater uncertainties are actually variable stars waiting for astronomers. Although these stars have not officially labeled the official Gaia group as such, Belokurov could compare these Gaia resources with past, completely reduced catalogs to prove that they are true. This should allow astronomers to quickly start data that they would have to wait until the next release of the data, a year or more to see.

Jo Bovy of the University of Toronto measured Oort's constants "while he waited for the files to be exhibited," says Hogg, who emphasizes the speed of natural science sprint. The constituents of Oorto, named after the same Jan Oort, who predicted the Oort cloud, are two figures that determine how the Milky Way rotates. They can be measured by looking at the large populations of stars in our home galaxy and studying how they move. With an initial release, Bovy calculated the number within minutes. "And he got better values ​​than they ever measured," says Hogg.

Hogg is a spear, how is the star's motion relative to the galaxy's disk related to its age. Astronomers have long known that stars achieve speed with age, but the exact ratio was difficult to figure out. This is a common problem with the ages; people, after all, do not live long enough to be born and die stars, but most astronomical age measurements are somewhat vague or strongly dependent on models. With Gaia's precision and its preliminary results, the next generation of astronomers can be the exact age for stars based exclusively on their speed, says Hogg.

Hogg says Gaia is not the only massive astronomical project to publish its information publicly. Kepler's mission and Sloan Digital Sky Survey, among other things, made publicly available their data, with the benefit of external users who turned hidden gems. When one researcher suggests or demands improvements in how data is processed or shared, Gaia team members can share benefits with all, as well as rewards themselves.

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But Hogg is rewarded by Gaia's mission, in particular Brown and Timo Prusti, for defending open access to data and for their unfavorable partnership with the scientific community to face inevitable issues before the survey reaches maturity. The result is a group effort in a group and the payout is more science for everyone.

Hogg plans future Gaia sprints: this year in Heidelberg in Germany and in New York in 2018. Gaia's primary task will not be completed by 2019. When the catalog is maturing, Gaia will discover explants with radial speed data and even a sharp look at the structure of the dairy roads.

"We've only seen the tip of the iceberg up to now," promises the Feet. With this great fresh science from the first edition, we can only wait to see the complete and glittering image of our Milky Way.


Korey Haynes is the contribution editor for Astronomy.


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