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 gentle years from Earth, virtually half the space to our neighboring galaxy, Andromeda, which is about 2.5 million gentle years away.

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

“This examine 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 massive, there’s hardly any space between the 2 galaxies.”

GuhaThakurta defined that the stellar halo element of our galaxy is far 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 midst of the disk is a central bulge, and surrounding it’s the halo, which accommodates the oldest stars within the galaxy and extends for a whole lot of 1000’s of sunshine years in each path.

“The halo is the toughest half to review 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 really accommodates many of the mass of the galaxy.”

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

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

“We had been in a position to make use of these variable stars as dependable tracers to pin down the distances,” Feng mentioned. “Our observations affirm the theoretical estimates of the dimensions of the halo, in order that’s an necessary outcome.”

The findings are based mostly on knowledge from the Subsequent Technology Virgo Cluster Survey (NGVS), a program utilizing the Canada-France-Hawaii Telescope (CFHT) to review a cluster of galaxies effectively 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 discipline, so the info we used are type of a by-product of that survey,” Feng defined.

Based on GuhaThakurta, the superb high quality of the NGVS knowledge enabled the staff to acquire probably the most dependable and exact characterization of RR Lyrae at these distances. RR Lyrae are previous stars with very particular bodily properties that trigger them to increase and contract in a usually repeating cycle.

“The way in which their brightness varies appears 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, if you happen to measure their common brightness, it’s the identical from star to star. This mix is incredible for learning the construction of the galaxy.”

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

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

This examine relies on observations obtained with MegaPrime/MegaCam, a joint undertaking 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.