Astronomers have found the most distant star in the Milky Way

Astronomers have discovered more than 200 distant variable stars known as RR Lyra in the starry halo of the Way lactic.

The most distant of these stars is more than a million light-years from Earth, almost half as far as our neighboring galaxy. Andromedawhich is about 2.5 million light-years away.

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Characteristic pulsations and brightness of stars RR Lyra make them excellent “standard candles” for measuring galactic distances. These new observations allowed researchers to trace the outer limits of the star’s halo. Milky Way.

“This study redefines what makes up the outer limits of our galaxy,” says Raja Guha-Thakurta, professor and chair of the Department of Astronomy and Astrophysics at the University of California, Santa Cruz (USA). “Our galaxy and Andromeda Both of them are so large that there is almost no space between the two galaxies.”

GuhaThakurta explains that the stellar halo component of our galaxy is much larger than the disk, which is about 100,000 light years in diameter. Our solar system is located in one of the spiral arms of the disk. In the middle of the disk is a central bulge, and around it is a halo that contains the oldest stars in the galaxy and extends hundreds of thousands of light-years in all directions.

“The halo is the hardest part to study because the outer boundaries are so far away,” says GuhaThakurta. “There are very few stars compared to the high density of stars in the disk and bulge, but the halo is dominated by dark matter.” actually contains most of the galaxy’s mass.”

Yuting Feng, a doctoral student working with Guha Thakurta at the University of California, California, has led the new study and will present his findings at an American Astronomical Society meeting.

According to Feng, previous studies have calculated that the stellar halo should extend about 300 kiloparsecs, or 1 million light-years, from the galactic center. 208 stars RR Lyra discovered by Feng and his colleagues were at a distance of 20 to 320 kiloparsecs.

“We were able to use these variable stars as reliable indicators to accurately determine distances,” says Feng. “Our observations confirm the theoretical estimates of halo size, so this is an important result.”

The findings are based on data from the Virgo Next Generation Cluster Survey (NGVS), a program that uses the Canada-France-Hawaii Telescope (CFHT) to study clusters of galaxies far beyond Earth. Milky Way. The survey was not designed to detect stars RR Lyra, so the researchers had 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 its surrounding galaxies, the telescope also captured foreground stars in the same field, so the data we used is kind of a by-product of this study,” Feng explains.

According to Guha Thakurta, the superior data quality of NGVS allowed the team to obtain the most reliable and accurate characterization RR Lyra at these distances. RR Lyra they are old stars with very specific physical properties that cause them to expand and contract in a regularly repeating cycle.

“The way their brightness changes is like an electrocardiogram – they are like the heartbeat of a galaxy – so the brightness quickly increases and slowly decreases, and the cycle repeats itself perfectly in a very characteristic way,” he explains. . “Besides, if you measure their average brightness, it is the same from star to star. This combination is fantastic for studying the structure of the galaxy.”

Here’s How They Were Discovered

The sky is full of stars, some brighter than others, but a star can appear bright because it’s so bright or because it’s so close, and it can be hard to tell the difference.

Astronomers can identify a star RR Lyra by its characteristic ripples, and then use its observed brightness to calculate how far away it is. However, the procedures are not easy. The most distant objects, such as quasars, can pass through stars RR Lyra.

“Only astronomers know how hard it is to get reliable tracers from such distances,” says Feng. RR Lyra Far distances give us a very powerful tool to study the halo and test our current models of the size and mass of our galaxy.”

This study is based on observations made with MegaPrime/MegaCam, a joint project between CFHT and CEA/IRFU, on the Canada-France-Hawaii Telescope (CFHT) operated by the National Research Council (NRC) of Canada, National Institute of Sciences. de l’Univers from the National Center for Scientific Research (CNRS) of France and the University of Hawaii. (Europe Press)

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