A group of astronomers has located more than 200 stars known as RR Lyrae in the galactic halo of the Milky Way, the most distant at more than a million light-years from Earth.
RR Lyrae are among the oldest stars in our galaxy and have physical properties that cause them to expand and contract in a regular cycle, allowing them to be used as a standard for measuring galactic distances.
A new study from the University of California at Santa Cruz, in the United States, will be presented at the meeting of the American Astronomical Society, which will take place in Seattle this week.
Observing these new RR Lyrae stars allowed the team to map the outer limits of the Milky Way’s halo, which is much larger than its disk and about 100,000 light-years across, according to Raja GuhaThakurta, an astrophysicist at the university.
The Milky Way and the neighboring galaxy, Andromeda, are so large that there is almost no space between the two galaxies, even though the latter is about 2.5 million light-years from our galaxy.
The Solar System is in one of the spiral arms of the Milky Way disk, in the middle of which is a central bulge, and around this is the halo, which contains the oldest stars and extends hundreds of thousands of light years to through all the directions.
The halo is the most difficult part to study because the outer limits are so far away and stars are few in number compared to the high densities of the disk and bulge.
The findings are based on data from the Virgo Cluster Next Generation Survey (NGVS), a program that uses the Canada-France-Hawaii Telescope (CFHT) to study a cluster of galaxies located far beyond the Milky Way.
The researchers had to search in detail for the data to detect the RR Lyrae stars among all those available in the NGVS, whose measurements are of “excellent quality”, which allowed them to obtain “the most reliable and precise characterization of the RR Lyrae in these distances”.
Source: TSF
