Astronomers find the most distant stars in our galaxy halfway to Andromeda

Astronomers have found greater than 200 distant variable stars generally known as RR Lyrae stars within the Milky Way’s stellar halo. Essentially the most distant of those stars is greater than 1,000,000 mild years from Earth, virtually half the gap to our neighboring galaxy, Andromeda, which is about 2.5 million mild years away.

The attribute pulsations and brightness of RR Lyrae stars make them glorious “customary candles” for measuring galactic distances. These new observations have allowed the researchers to hint the outer limits of the Milky Way’s halo.

“This research is redefining what constitutes the outer limits of our galaxy,” mentioned Raja GuhaThakurta, professor and chair of astronomy and astrophysics at UC Santa Cruz. “Our galaxy and Andromeda are each so huge, there’s hardly any space between the 2 galaxies.”

GuhaThakurta defined that the stellar halo part of our galaxy is way greater than the disk, which is about 100,000 light years throughout. Our solar system resides in one of many spiral arms of the disk. In the course of the disk is a central bulge, and surrounding it’s the halo, which accommodates the oldest stars within the galaxy and extends for tons of of hundreds of sunshine years in each route.

“The halo is the toughest half to check as a result of the outer limits are so distant,” GuhaThakurta mentioned. “The celebs are very sparse in comparison with the excessive stellar densities of the disk and the bulge, however the halo is dominated by dark matter and truly accommodates a lot of the mass of the galaxy.”

Yuting Feng, a doctoral pupil working with GuhaThakurta at UCSC, led the brand new research and is presenting their findings in two talks on the American Astronomical Society assembly in Seattle on January 9 and 11.

In keeping with Feng, earlier modeling research had calculated that the stellar halo ought to prolong out to round 300 kiloparsecs or 1 million mild years from the galactic heart. (Astronomers measure galactic distances in kiloparsecs; one kiloparsec is the same as 3,260 mild years.) The 208 RR Lyrae stars detected by Feng and his colleagues ranged in distance from about 20 to 320 kiloparsecs.

“We had been ready to make use of these variable stars as dependable tracers to pin down the distances,” Feng mentioned. “Our observations verify the theoretical estimates of the scale of the halo, in order that’s an vital consequence.”

The findings are based mostly on information from the Subsequent Technology Virgo Cluster Survey (NGVS), a program utilizing the Canada-France-Hawaii Telescope (CFHT) to check a cluster of galaxies nicely past the Milky Way. The survey was not designed to detect RR Lyrae stars, so the researchers needed to dig them out of the dataset. The Virgo Cluster is a big cluster of galaxies that features the enormous elliptical galaxy M87.

“To get a deep publicity of M87 and the galaxies round it, the telescope additionally captured the foreground stars in the identical area, so the info we used are form of a by-product of that survey,” Feng defined.

In keeping with GuhaThakurta, the wonderful high quality of the NGVS information enabled the crew to acquire probably the most dependable and exact characterization of RR Lyrae at these distances. RR Lyrae are outdated stars with very particular bodily properties that trigger them to increase and contract in a frequently repeating cycle.

“The way in which their brightness varies seems to be like an EKG—they’re just like the heartbeats of the galaxy—so the brightness goes up rapidly and comes down slowly, and the cycle repeats completely with this very attribute form,” GuhaThakurta mentioned. “As well as, for those who measure their common brightness, it’s the similar from star to star. This mix is improbable for learning the construction of the galaxy.”

The sky is filled with stars, some brighter than others, however a star could look shiny as a result of it is vitally luminous or as a result of it is vitally shut, and it may be arduous to inform the distinction. Astronomers can establish an RR Lyrae star from its attribute pulsations, then use its noticed brightness to calculate how distant it’s. The procedures aren’t easy, nevertheless. Extra distant objects, comparable to quasars, can masquerade as RR Lyrae stars.

“Solely astronomers understand how painful it’s to get dependable tracers of those distances,” Feng mentioned. “This sturdy pattern of distant RR Lyrae stars offers us a really highly effective device for learning the halo and testing our present fashions of the scale and mass of our galaxy.”

This research relies on observations obtained with MegaPrime/MegaCam, a joint challenge of CFHT and CEA/IRFU, on the Canada-France-Hawaii Telescope (CFHT), which is operated by the Nationwide Analysis Council (NRC) of Canada, the Institut Nationwide des Sciences de l’Univers of the Centre Nationwide de la Recherche Scientifique (CNRS) of France, and the College of Hawaii.