Our galaxy, the Milky Way, is an enormous island of billions of stars. The nice majority of these stars reside in the principle disk of the galaxy itself, however there are others farther out as nicely. Actually, some stars are method out within the Milky Way’s stellar halo. The halo surrounds the principle galaxy and is extra diffuse but in addition a lot bigger than our galaxy’s major disk. This month, scientists stated they’ve found 208 new variable stars referred to as RR Lyrae stars on this halo. Certainly, they’re extremely distant; the farthest ones are over 1,000,000 light-years distant, reaching almost midway to the Andromeda galaxy.
Yuting Feng, a doctoral pupil at UC Santa Cruz, led the brand new examine and presented the findings on the 241st Meeting of the American Astronomical Society in Seattle on January 11.
Milky Way’s farthest stars and the stellar halo
The newly discovered stars are within the very outermost a part of our galaxy, the stellar halo. And this halo is large. Extra particularly, earlier research point out it extends 300 kiloparsecs or 1 million light-years from the galactic heart. One kiloparsec equals 3,260 light-years. Correspondingly, the 208 RR Lyrae stars vary in distance from about 20 to 320 kiloparsecs. Extremely, the farthest ones prolong midway to the neighboring Andromeda galaxy. Feng said:
We had been ready to make use of these variable stars as dependable tracers to pin down the distances. Our observations verify the theoretical estimates of the scale of the halo, in order that’s an necessary end result.
We consider our galaxy because the brightest disk of stars that we see in photographs and laptop simulations (since we are able to’t really go above to look down on it). However actually, nevertheless, the outermost fringes prolong a lot farther than that. Certainly, a minimum of midway to the following massive galaxy, it seems.
The outer limits of our galaxy
As Puragra (Raja) GuhaThakurta, one of many lead authors and professor and chair of astronomy and astrophysics at UC Santa Cruz, stated:
This examine is redefining what constitutes the outer limits of our galaxy. Our galaxy and Andromeda are each so massive, there’s hardly any space between the 2 galaxies.
The halo is the toughest half to review as a result of the outer limits are so distant. 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 comprises a lot of the mass of the galaxy.
Subsequent Technology Virgo Cluster Survey
Because it occurred, the invention of the RR Lyrae stars was the results of a unique form of statement. The researchers used the Subsequent Technology Virgo Cluster Survey (NGVS), a program on the Canada-France-Hawaii Telescope (CFHT), to review a gaggle of galaxies method out past the Milky Way. For instance, this cluster consists of the enormous elliptical galaxy Messier 87 (M87).
Despite the fact that NGVS isn’t designed to search out RR Lyrae stars, the celebrities had been within the knowledge, ready to be discovered. On this case, the researchers discovered them as a result of NGVS had taken deep-exposure photos of the galaxies. As Feng defined:
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 information we used are kind of a by-product of that survey.
Because of this, the information is the perfect astronomers have ever obtained of those stars at such immense distances.
Milky Way’s farthest stars pulsate like a cosmic heartbeat
RR Lyrae stars are very previous stars generally known as variable stars. They broaden and contract in a daily cycle, form of like a cosmic heartbeat. GuhaThakurta stated:
The way in which their brightness varies appears to be like 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. As well as, when you measure their common brightness, it’s the identical from star to star. This mixture is unbelievable for learning the construction of the galaxy.
Scientists suppose that almost all RR Lyrae stars are singular, with no companion, like our sun. In 2015, nevertheless, astronomers announced discovering 20 RR Lyrae star programs that had been binary (consisting of two stars). That’s a small quantity, nevertheless it’s nonetheless a rise of two,000% from earlier estimates.
Historical past and evolution of our galaxy
The invention of those distant RR Lyrae stars reveals clues as to the historical past and formation of our galaxy, together with the halo. The paper states:
The Milky Way’s stellar halo holds preserved proof of the formation historical past and evolution of the galaxy … The attribute gentle curve shapes of RR Lyrae and the truth that they’re glorious customary candles makes these stars dependable tracers of the Milky Way halo and Local Group.
Testing present fashions of the Milky Way
The RR Lyrae stars additionally present precious perception into the scale and mass of the Milky Way. As Feng famous:
Solely astronomers understand how painful it’s to get dependable tracers of those distances. This sturdy pattern of distant RR Lyrae stars provides us a really highly effective instrument for learning the halo and testing our present fashions of the scale and mass of our galaxy.
Backside line: Astronomers have found the Milky Way’s farthest stars in our galaxy’s large stellar halo. Essentially the most distant stars are over 1,000,000 light-years away, nearly midway to the Andromeda galaxy.
