Within our galaxy, there are thousands of stars orbiting the center of the Milky Way at high speed. Sometimes some of them accelerate so much that they free our galaxies and become intergalactic objects. Due to extreme dynamic and astrophysical processes, astronomers are most interested in studying these stars – especially those capable of reaching escape speeds and leaving our galaxy.
However, an international team of astronomers led by the National Astronomical Observatory of China (NAOC) recently announced the discovery of 591 high-speed stars. Based on data provided by a multi-object spectroscopic telescope with large sky-high objects (LAMOST) and ESAs Gaia Observatory, indicated that 43 of these stars are fast enough to one day escape the Milky Way.
The study was published in Astrophysical Journal Supplement Series on 17 Decemberth. The study was led by Dr. LI Yinbi, an astronomer at the NAOC, and included researchers from the Chinese Academy of Sciences (CAS), the Max-Planck Institute for Astronomy (MPIA), the Institute for Advanced Studies, the European Southern Observatory (ESO), ExtantFuture Technology Co., Institute of Statistical Mathematics in Tokyo and several universities.
As for astrophysical studies, high-speed stars are a relatively recent discovery. It was first observed in 2005, and over the next 15 years more observatories were discovered over 550. From them, astronomers were able to derive four subclasses of high-speed stars, which include: hyperfast stars, fugitive stars, hyperrun stars, and fast halo stars.
Then this last discovery is especially significant because it effectively doubles the number of known high-speed stars, which are quite rare in our galaxy. “This time, 591 high-speed stars discovered doubled the total number previously discovered, bringing the current total to more than 1,000,” Dr. Lee said.
Hyperspeed stars (HVS), the fastest of the pile, are particularly interesting because they have achieved relativistic velocities (a fraction of the speed of light). In fact, astronomers have estimated that with the right kind of gravitational acceleration, star speeds can reach 1/10th up to 1/3rd speed of light – approximately 30,000 to 100,000 km / s (18,640 to 62,130 mi / s).
It is these stars that are the speed of flight needed to leave the Milky Way. Said prof. LU Youjun from NAOC, co-author of this paper:
“Although rare in the Milky Way, high-speed stars, with unique kinematics, can provide deep insight into a wide range of galactic science, from a central supermassive black hole to a distant galactic halo.”
“Rare” is certainly an appropriate description. According to previous estimates by astrophysicists, there will probably be only 1000 HVS in our galaxy (that is 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 the many cosmic mysteries.
For its study, the international relied in part on LAMOST data. In addition to being the largest optical telescope in China, LAMOST also has the highest spectral collection rate of any telescope in the world and can observe about 4,000 celestial objects in a single exposure. Since starting the survey in 2012, it has established the largest spectrum database in the world.
In addition, the team relied on the astrometric measurements it conducted Gaia Observatory, launched by the European Space Agency (ESA) in 2013. Since then, it has collected data on the position, proper motion and speed of over 1.3 billion celestial objects, making it the largest astrometric database in the world. Both the observatories and their mass databases were invaluable in the detection and study of CVC.
Based on the movement and composition of the objects they observed, the research team identified 591 CVCs originating from the inner halo of the Milky Way. “Their low metal content indicates that the majority of the stellar halo was formed as a result of the accumulation and disturbance of the tides of dwarf galaxies,” said co-author Prof. Zhao Gang from CAS School of Astronomy and Space.
One of the biggest exceptions to this study is the way it shows how combining multiple large studies can lead to the discovery of rare objects. In the future, astronomers will be able to draw from even larger databases containing survey data provided by next-generation instruments. This data will be especially useful in studying Dark Matter, a mysterious mass that makes up 27% of the mass energy density of the Universe.
By monitoring the movement of CVC, astrophysicists will be able to better limit the shape of the halo of dark matter of the Milky Way. In addition, they could tell us a lot about the origin and evolution of the Milky Way itself, as HVS is believed to be the result of galactic fusions and other extreme gravitational forces (i.e., supermassive holes). Having more to study could therefore help astronomers create a history of past galactic mergers.
It has also been undertaken that CVC could allow astrophysicists to accurately limit the mass of our galaxy, something that remains unresolved. On top of all that, previous research has suggested that CVC may carry its planetary systems with it, which could be one way of expanding life through the cosmos (intergalactic panspermia).
Further reading: Chinese Academy of Sciences,, Astrophysical Journal