What astronomers have already learned from the new map of the Milky Way from the Gaia space telescope

Original author: Natalie Wolchover
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Review of some of the most important discoveries made on the basis of the new map of the Galaxy, obtained by the Gaia Observatory

The heavenly map of the Milky Way and its satellites, created by Gaia based on measurements of nearly 1.7 billion stars.

On April 25, Teresa Antoia from the University of Barcelona became one of thousands of astronomers who downloaded and began to study the new complete map of the Milky Way created by the European Space Agency's Gaia . Less than a day, as they and their colleagues reported the discovery of unprecedented substructures across the galaxy: “Forms in the form of arches, snail shells and mountain ranges,” they wrote, each of which gives hints of the mysterious past of the Milky Way.

The work of Anthoy is one of the whole work flow, which began after the long-awaited second data output from the Gaia satellite, launched in 2013, and has since marked the location, brightness and colors of 1.7 billion stars of the Milky Way, as well as speeds of 1.3 billion from these stars. (In September 2016, the satellite team released the first map, on which the location and brightness of only 1.1 billion stars were marked). The astronomers, who previously had a catalog containing 2.5 million brightest stars in the galaxy, welcome the new era of precise astronomy. And here are the most important discoveries made on the basis of new data.

Star streams

The French team applied the pre-prepared STREAMFINDER [stream search] algorithm to Gaia's data, and immediately found a rich network of “star streams” moving together inside and around the Milky Way stars. “The idea is to track the movement of these flows back in time and study the past of the Galaxy and the history of its formation,” said Kiati Malkhan of the University of Strasbourg, the lead author of the work describing these discoveries in the field of “galactic archeology”.

The abundance of stellar streams — which are considered to be consequences of small satellite galaxies and star clusters drawn in by gravity — can potentially solve the “problem of missing satellites”, the question of why only about 50 satellite galaxies are observed around the Milky Way, despite the fact that simulations of galaxy formation are hundreds of them. Another mystery is why the satellites of the Milky Way are in the same plane, although the simulations suggest that they should have been formed from all sides. Malkhan and his colleagues hope to clarify or resolve this problem with the plane by “statistical analysis of the structure and dynamics of a large set of flows”. Star streams in the northern and southern hemisphere; color denotes their flow rate. Another group used Gaia’s data to

detailed study of the longest galactic streams. Apparently, the motion of some stars was disturbed by shreds of invisible dark matter, which suggests that these streams can be used to build a map of dark matter substructures throughout the galaxy.

Speed ​​dwarfs

For decades, astrophysicists have argued about the origin of type Ia supernovae - explosions of stars that serve as "standard candles" for estimating space distances. Using data from Gaia and subsequent observations from the telescope, Ken Scheen of the University of California at Berkeley and colleagues found convincing evidence of the theory of dynamically developed double-degenerate double detonation (D6).

Scenario D6 begins with two white dwarfs — the dense cores of dead stars, the size of a planet — in close mutual orbit. According to the theory, a more massive dwarf should begin to tear matter away from a less massive one, moreover so quickly and violently, that part of the helium in the transient matter explodes. This explosion generates a carbon and oxygen explosion in a more massive dwarf, causing it to explode, generating supernova Ia. The second white dwarf, since it is no longer holding, breaks down and flies into space with great speed.

Among the data, Gaia Schoen and his colleagues found three “superfast white dwarfs” hurrying across the galaxy at speeds of more than 1000 km / s, which is enough to break out of its gravitational pull. They claim that their discovery provides a “preliminary confirmation” of the D6 scenario. In the letter, Sheen said that understanding the history of type Ia supernovae will reduce uncertainties in space measurements and chemical enrichment models of galaxies with supernova explosions.

Small galaxy, big black hole

British astronomers tracked the origin of another superfast star, which, as it turned out, comes from the center of the Large Magellanic Cloud , the largest satellite galaxy of the Milky Way. And this can only mean one thing: the fact that the star was accelerated due to the effect of the sling, passing by a massive black hole in the center of the Large Magellanic Cloud. In the centers of full-size galaxies, huge black holes almost always lurk, the origin of which remains a mystery. Their presence in some small galaxies clarifies the riddle.

Stars spinning clockwise around the center of the Large Magellanic Cloud, the largest galaxy of the Milky Way satellite

Trouble with Hubble

In 1998, Adam Riesz and other astronomers, based on the distances to type Ia supernovae, suggested that the Universe expands with acceleration under the influence of "dark energy." Interestingly, about the exact rate of expansion (known as the “ Hubble constant ”) estimates based on supernovae differ by 8% from estimates based on light coming from the early Universe, even if we take into account the acceleration given by dark energy since then This is one of the greatest mysteries of cosmology.

Now Riess and colleagues used Gaia's data to more accurately measure distances to Cepheids , which allow them to calibrate distances to type Ia supernovae. This allowed them make the most accurate measurements of the Hubble constant using supernovae, which only increased the divergence of these estimates from observations of the early Universe.

Galactic revolution

While many researchers are studying the diverse stellar population and the dynamics of the Galaxy, Laura Watkins of the Space Research Institute using the space telescope and her colleagues used the movements of star clusters moving along orbits in the Milky Way to estimate the mass of the Galaxy . They say that, given the dark matter, it is about 1.5 trillion solar masses. Joshua Simon of the Carnegie Institute of Science analyzeda remote population of satellite galaxies, and found that they are all at the closest distance in their orbits around the Milky Way. This coincidence seems “strange,” as Simon wrote in a letter. “I don’t think we had enough time to figure out all the consequences of this result.” "We know that the data from Gaia will produce a revolution," added Simon. And astronomers will reap their fruits in the next few years.

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