Astronomers discover hundreds of stars at high speed, many of them emerging from the Milky Way

In our galaxy, there are thousands of stars that orbit the center of the Milky Way at high speeds. Occasionally, some of them gain so much speed that they break free from our galaxy and become intergalactic objects. Because of the extreme dynamic and astrophysical processes involved, astronomers are more interested in studying these stars – especially those that are capable of reaching flight speed and leaving our galaxy.

However, an international team of astronomers led by the National Astronomical Observatories of China (NAOC) recently announced the discovery of 591 stars at high speed. Based on data provided by the Large Sky Area Multi-Object Spectroscopic Fiber Telescope (LAMOST) and ESA Gaia Observatory, they indicated that 43 of these stars are fast enough to one day escape the Milky Way.

The study was published in The Astrophysical Journal Supplement Series December 17th^e. The study was led by Dr. LI Yinbi, an astronomer from NAOC, and included researchers from the Chinese Academy of Sciences (CAS), the Max-Planck Institute for Astronomy (MPIA), the Institute for Advanced Studies, European Southern Observatory (ESO). ), ExtantFuture Technology Co., Tokyo Institute of Statistical Mathematics, and several universities.

In terms of astrophysical studies, high speed stars are a relatively recent discovery. The first was observed in 2005 and over the following 15 years, more than 550 were discovered by several observatories. From these, astronomers were able to derive four subclasses of high-speed stars, which include: hypervelocity stars, fleeing stars, hyper-runaway stars, and fast halo stars.

This latest discovery is all the more significant as it effectively doubles the number of known high-speed stars, which are quite rare in our galaxy. “The 591 high-speed stars discovered this time have doubled the total number previously discovered, bringing the current total number to more than 1,000,” said Dr Li.

Of particular interest are the hypervelocity stars (HVS), the fastest of the group, because they have reached relativistic speeds (a fraction of the speed of light). In fact, astronomers have estimated that with the right kind of gravitational acceleration, hyperspeed stars can reach 1/10^e at 1/3^rd the speed of light – about 30,000 to 100,000 km / s (18,640 to 62,130 mph).

It is these stars that have the necessary flight speed to leave the Milky Way. NAOC’s Professor LU Youjun, co-author of this article, said:

“Although rare in the Milky Way, high-speed stars, with unique kinematics, can provide in-depth insight into a wide range of galactic sciences, from the central supermassive black hole to the distant galactic halo.

“Rare” is certainly an apt description. According to previous estimates made by astrophysicists, there will probably only be 1000 HVS in our galaxy (or 0.0000005% of the galactic population). But given their speed and the vast distances they travel, tracking these stars and creating a database of their movements could tell us a lot about a number of cosmic mysteries.

For the sake of their study, the international team relied in part on the data provided by LAMOST. Besides being the largest optical telescope in China, LAMOST has the highest spectral acquisition rate of any telescope in the world and can observe around 4,000 celestial objects in a single exposure. Since he started conducting surveys in 2012, he has established the largest spectral database in the world.

In addition, the team relied on astrometric measurements made by the Gaia Observatory, which was launched by the European Space Agency (ESA) in 2013. Since then it has gathered information on the location, correct movement and speed of more than 1.3 billion celestial objects, making it makes the largest astrometric database in the world. Both observatories and their massive databases have been invaluable in detecting and studying HVS.

Based on the movement and composition of the objects they observed, the research team identified 591 HVS from the internal halo of the Milky Way. “Their low metallities indicate that most of the stellar halo formed as a result of accretion and disturbance of the tides of dwarf galaxies,” said co-author Professor Zhao Gang of the CAS School of Astronomy and Space Science.

One of the biggest lessons from this study is how it shows how the combination of several large investigations can lead to the discovery of rare objects. In the future, astronomers will be able to tap into even larger databases containing survey data provided by next-generation instruments. These data will be particularly useful in the study of dark matter, the mysterious mass that constitutes 27% of the mass-energy density of the Universe.

By following the movement of the HVS, astrophysicists will be able to better constrain the shape of the dark matter halo of the Milky Way. Moreover, they could tell us a lot about the formation and evolution of the Milky Way itself, as the HVS is believed to be the result of galactic fusions and other extreme gravitational forces (i.e. . Supermassive holes). Having more to study, therefore, could help astronomers create a history of past galactic mergers.

It has also been ventured that HVS could allow astrophysicists to precisely constrain the mass of our galaxy, which remains unresolved. On top of all of this, previous research has indicated that HVS can carry their planetary systems with them, which could be one of the ways that life spreads throughout the cosmos (intergalactic panspermia).

Further reading: Chinese Academy of Sciences, The astrophysical journal