Ariel Eisenhandler
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A new dwarf galaxy has been discovered orbiting the Milky Way
Large spiral galaxies, such as the Milky Way, are like continents stretching out into space, and like any continent these galaxies should have many islands spread along their shores. Current models of galaxy formation suggest that a galactic continent should have more neighboring "islands" than what can be seen through a telescope. Now another island has been added to the representation of the Milky Way, small enough to contradict predictions about the mapping of the Milky Way. Other dwarfs, such as the one recently discovered in the Big Dipper group (better known as the Big Dipper), will follow.
The recently discovered dwarf galaxy Ursa Major, located just over 300 light years from us in the direction of the Big Dipper, has a surface brightness equal to one-tenth that of the next dwarf galaxy in the Milky Way (located in the sextant direction, constellation, constellation in the southern sky). Like the galaxy in the sextant, the galaxy in the Big Wheel is spherical in shape (a dSph galaxy type) and largely resembles globular clusters, which are found in close proximity to large spiral galaxies.
According to Beth Willman (Beth Willman) from New York University, who acts as the lead researcher in a group of 15 astronomers who examine the data obtained from the "Sloan Digital Sky Survey-SDSS- additional details and Alfred Sloan ). "The large cart is old and low in metals, like all the known elliptical dwarfs that accompany the Milky Way. If so, it could be 10 times fainter than the faintest known satellite of the Milky Way. We are in the process of obtaining more detailed observations, which will provide a more detailed picture of the Big Dipper, and which will then be compared to the other known satellites."
"The Milky Way galaxy was discovered as part of a systematic mapping of the companions of the Milky Way. It was revealed as a slight statistical change in the number of red stars in this region of the sky." Beth adds.
All galaxies and star clusters include in their composition a wide variety of star types. These include blue giants, which are young, massive stars with short lifespans and very high luminosity; dim yellow stars, which are less massive and have a long lifespan and are usually in the middle of their lives, like our sun; and red giants, which are old stars at the end of their lives with moderate brightness and very swollen, such as Antares in the Scorpius group and Betelgeuse in the Orion group. When it comes to finding neighboring dwarf galaxies, such as the one in the Big Dipper, the latter type of star has an important benefit. Red giants are bright enough to be discovered, spectroscopically identified and counted by automatic sky scanning telescopes like the SDSS in New Mexico, even small satellite galaxies located hundreds or thousands of light years away.
Once data from the SDSS is available, teams like Beth's analyze it to find high concentrations of red giants in small regions of the sky. Their presence could indicate the existence of a dwarf galaxy or an unexpected globular cluster. By spectrographic information it is possible to filter out fainter, but closer, red giants within the Milky Way. Finally, a more detailed view of the study can be obtained by using more sensitive instruments in other observatories.
Once the information showed that the existence of a dwarf galaxy in the Big Dipper was possible, the wide-field camera (diameter: 2.5 meters) of the Isaac Newton Telescope in the Canary Islands helped to determine its general appearance. Images from the Newtonian telescope and information from the SDSS were combined to verify the nature of the study as an elliptical galaxy and not just an errant globular cluster, like the intergalactic wanderer (NGC 2419) in the Lynx group, located at approximately the same distance in space.
Although small dwarf galaxies have an absolute luminosity similar to that of the brightest globular clusters, there is one important difference between them: size. The dwarf galaxy in the Big Dipper is about 10 times larger than the largest known globular cluster. It is very likely that most of its mass is non-stellar matter, "dark matter", while almost all the mass in a globular cluster is packed in stars. Because it's big, but not that bright, the team labeled the Big Carriage a dwarf galaxy.
From a cosmological point of view, satellite galaxies, such as the one in the Big Dipper (of the dSph type), play an important role in explaining the formation of large, medium and small structures throughout the universe. On large scales, spiral galaxies (such as our Milky Way or the Andromeda Galaxy) are known to reside in groups of galaxies called groups or clusters. Our group (the LOCAL GROUP) is small in mass and size while its two largest companions, although large by spiral galaxy standards, are quite modest compared to the largest known galaxies (giant ellipticals). The largest scale of galactic structure in the universe includes thousands of large galaxies while our local group includes only a few dozen. At the smallest scale, the Milky Way and its companions, which include the two irregular galaxies "Magellanic Clouds" as well as 10 dwarf elliptical galaxies, form a single gravitational boundary. Because of these reasons, astronomers have the opportunity to study the smallest possible building blocks of intergalactic structure.
In their article called "A New Dwarf Galaxy for the Milky Way, in the Big Dipper" Beth and her team add: "The Big Dipper galaxy was discovered very close to our detection limits. It is very possible that many other dwarf galaxies, with characteristics similar to or fainter than those of the Big Dipper galaxy, exist around the Milky Way... It is reasonable to expect that another 9-8 dwarf galaxies around the sky, brighter than our detection limits, have not yet been discovered. If this is true, this number will rule out (in terms of galactic structure) models that do not predict the presence of very dim dwarf galaxies."
For the article in Universe Today
Abridged version by Avi Blizovsky
Some of the latest models of galaxy formation predict that large spiral galaxies such as the Milky Way and Andromeda should attract many more dwarf satellite galaxies than have actually been recorded. Many of the halo galaxies should be smaller than those already discovered. Astronomers examining data from the Sloan Digital Sky Survey (SDSS) have added a tenth satellite galaxy to the Milky Way, and this time it's particularly easy.
The new galaxy is located 300 thousand light years from us in the direction of the Big Dipper and has been named URSA MAJOR - Uma. Its surface brightness is only one-tenth that of the next-largest dwarf galaxy (located in Sextans). Like its older sister Masextens, Uma has a globular shape and is somewhat similar to the globular clusters that accompany other large spiral galaxies.
According to New York University's Beth Williams, lead researcher on a team of 15 astronomers studying the SDSS data: Ursa Major appears ancient and metal-poor, like all of the Milky Way's globular companion galaxies. We are now in the process of obtaining more detailed observations that will provide a better picture of Umma's properties, and then compare it to the other known satellite galaxies.
In the article, Williams writes that Uma was really borderline in terms of the detection ability of the devices, and it is possible that they will find 8-9 more like it.
Yadan Astrophysics 4 - Galaxies
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