American astronomers find tiny galaxy
Baku, January 20 (AZERTAC). Astronomers have discovered a small galaxy that is invisible to telescopes and may be completely composed of dark matter, which reflects no light.
The newfound galaxy is incredibly distant and extremely small. It orbits as a satellite of a larger galaxy. Though telescopes can't spot the dwarf galaxy, scientists detected its presence through the tiny distortions its gravity causes to light that passes it by.
Scientists think dark matter, which may be made of some exotic particle that doesn't reflect light, makes up about 98 percent of all matter in the universe. Yet it has never been detected directly. Discovering dark objects like this tiny, distant galaxy could help researchers understand better what dark matter is and how it affects regular matter around it.
The new dwarf galaxy is about 7 billion light-years away, meaning its light has taken 7 billion years to reach us here on Earth. It weighs about 190 million times the mass of the sun — a seemingly hefty sum, although typical galaxies pack in the mass of tens of billions of suns.
"This is the lowest mass galaxy that we've seen at this distance by far," said study co-author Matthew Auger of the University of California, Santa Barbara.
Even farther away, at about 10 billion light-years, is another galaxy whose light passes by the dark dwarf and its host on its way to Earth. As this light travels through space, it is bent by the gravity of the intervening galaxy and its satellite, causing a distorted, curved picture called an "Einstein ring," after the famous scientist, who predicted such warping effects in his general theory of relativity.
Though most of this warping is caused by the larger gravitational tug of the host galaxy, researchers used a computer model to detect a slight excess of warping caused by the tiny addition of the dwarf satellite's gravity.
"It`s a subtle effect that by eye you would tend not to see except from subtracting a model from the data," Auger told SPACE.com.
The astronomers were also helped by extremely high-resolution images taken by the Keck Observatory in Hawaii, using a system called adaptive optics to compensate for atmospheric blurring.
"The image quality in the data we used here is somewhat better than the quality you can get from the Hubble Space Telescope," Auger said.
Auger and his colleagues, led by Simona Vegetti of MIT, reported their finding in the Jan. 19 issue of the journal Nature.
Hidden stars?
Because it is so far and hard to see, astronomers can`t be sure if the newly discovered galaxy really is made almost exclusively of dark matter, or if it just contains stars that are too dim to be visible at this distance.
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