A halo is a round cloud of stars surrounding a galaxy. In the middle of the disk is a main bulge, and surrounding it is the halo, which includes the oldest stars in the galaxy and extends for hundreds of thousands of light years in every instructions.
The 208 RR Lyrae stars discovered by Feng and his coworkers ranged in range from about 20 to 320 kiloparsecs.
“In addition, if you determine their average brightness, it is the same from star to star. The sky is complete of stars, some brighter than others, however a star might look bright because it is really luminous or due to the fact that it is really close, and it can be tough to tell the distinction.
” This research study is redefining what makes up the outer limitations of our galaxy,” said Raja GuhaThakurta, professor and chair of astronomy and astrophysics at UC Santa Cruz. “Our galaxy and Andromeda are both so huge, theres hardly any space in between the 2 galaxies.”.
GuhaThakurta discussed that the stellar halo part of our galaxy is much bigger than the disk, which has to do with 100,000 light-years across. Our solar system resides in one of the spiral arms of the disk. In the middle of the disk is a central bulge, and surrounding it is the halo, which consists of the oldest stars in the galaxy and extends for numerous thousands of light years in every direction.
” The halo is the hardest part to study because the external limits are up until now away,” GuhaThakurta stated. “The stars are very sporadic compared to the high stellar densities of the disk and the bulge, but the halo is dominated by dark matter and in fact consists of many of the mass of the galaxy.”.
Yuting Feng, a doctoral student dealing with GuhaThakurta at UCSC, led the new study and presented their findings in 2 talks at the American Astronomical Society conference in Seattle on January 9 and 11.
According to Feng, previous modeling studies had actually calculated that the excellent halo should extend out to around 300 kiloparsecs or 1 million light years from the galactic center. (Astronomers measure stellar ranges in kiloparsecs; one kiloparsec is equivalent to 3,260 light years.) The 208 RR Lyrae stars detected by Feng and his colleagues ranged in range from about 20 to 320 kiloparsecs.
” We had the ability to use these variable stars as reliable tracers to select the distances,” Feng stated. “Our observations validate the theoretical price quotes of the size of the halo, so thats an essential result.”.
The findings are based on information from the Next Generation Virgo Cluster Survey (NGVS), a program utilizing the Canada-France-Hawaii Telescope (CFHT) to study a cluster of galaxies well beyond the Milky Way. The survey was not created to detect RR Lyrae stars, so the researchers needed to dig them out of the dataset. The Virgo Cluster is a large cluster of galaxies that includes the giant elliptical galaxy M87.
” To get a deep exposure of M87 and the galaxies around it, the telescope likewise captured the foreground stars in the exact same field, so the data we used are sort of a spin-off of that study,” Feng described.
According to GuhaThakurta, the exceptional quality of the NGVS data made it possible for the team to get the most precise and reliable characterization of RR Lyrae at these ranges. RR Lyrae are old stars with really particular physical properties that cause them to contract and expand in a routinely repeating cycle.
” The way their brightness differs appears like an EKG– theyre like the heartbeats of the galaxy– so the brightness increases quickly and boils down slowly, and the cycle repeats perfectly with this extremely characteristic shape,” GuhaThakurta said. “In addition, if you measure their average brightness, it is the exact same from star to star. This combination is wonderful for studying the structure of the galaxy.”.
The sky is full of stars, some brighter than others, but a star may look brilliant because it is extremely luminous or because it is very close, and it can be hard to tell the difference. Astronomers can determine an RR Lyrae star from its particular pulsations, then utilize its observed brightness to determine how far away it is.
” Only astronomers understand how unpleasant it is to get dependable tracers of these ranges,” Feng said. “This robust sample of far-off RR Lyrae stars offers us a very effective tool for studying the halo and screening our existing designs of the size and mass of our galaxy.”.
This study is based upon observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/IRFU, at the Canada-France-Hawaii Telescope (CFHT), which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de lUnivers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii.
Satisfying: AAS 241.
This illustration reveals the Milky Way galaxys inner and external halos. A halo is a spherical cloud of stars surrounding a galaxy. Credit: NASA, ESA, and A. Feild (STScI).
A look for variable stars called RR Lyrae has actually discovered some of the most distant stars in the Milky Ways halo a million light years away.
Astronomers have found more than 200 far-off variable stars called RR Lyrae stars in the Milky Ways stellar halo. The most far-off of these stars are more than a million light-years from Earth, practically half the range to our neighboring galaxy, Andromeda, which is about 2.5 million light-years away.
The characteristic pulsations and brightness of RR Lyrae stars make them outstanding “standard candle lights” for determining galactic ranges. These new observations allowed the researchers to trace the external limits of the Milky Ways halo.