ULAS J0015+01 is the designation given to a star discovered on July 10, 2014 as the farthest star in bound of the gravitational attraction of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye ...

galaxy. It is estimated to lie at 900,000 light-years from the Earth, beyond the reaches of the Magellanic Clouds. Another star, ULAS J0744+25, was a bit closer. These stars are thought to be remnants of either the Milky Way's creation, or the merging of it with another small galaxy.

Discovery

ULAS J0015+01 was discovered on the 10th of July, 2014 with the

UKIRT Infrared Deep Sky Survey The UKIRT Infrared Deep Sky Survey or UKIDSS is an astronomical survey conducted using the WFCAM wide field camera on the United Kingdom Infrared Telescope on Mauna Kea in Hawaii. Survey observations were commenced in 2005. UKIDSS consists of f ...

and the

Sloan Digital Sky Survey The Sloan Digital Sky Survey or SDSS is a major multi-spectral imaging and spectroscopic redshift survey using a dedicated 2.5-m wide-angle optical telescope at Apache Point Observatory in New Mexico, United States. The project began in 2000 a ...

. Both of these stars being cool

red giant A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses ()) in a late phase of stellar evolution. The outer atmosphere is inflated and tenuous, making the radius large and the surface temperature around or ...

s, they are extremely bright which is one of the key factors in their discovery. Their distance was estimated with a number of different techniques, which all pointed towards 900,000 light years away.

Distance

ULAS J0015+01 is, at the current time, 900,000 light years away from the Milky Way galaxy. The Milky Way's disk is 180,000 light years in diameter, putting it far beyond the Milky Way stellar disk, or only 3 times closer than the Andromeda galaxy. In comparison, in distance to the Milky Way's satellite galaxy, the

Large Magellanic Cloud The Large Magellanic Cloud (LMC), or Nubecula Major, is a satellite galaxy of the Milky Way. At a distance of around 50 kiloparsecs (≈160,000 light-years), the LMC is the second- or third-closest galaxy to the Milky Way, after the ...

, is only 160,000 light-years from Earth. ULAS J0015+01 and ULAS J0744+25 are not technically in a galaxy, but they are both classified as being in the Milky Way's outer halo, which stretches at least 500,000 light years away. These stars were both the first to be discovered beyond 200 kpc.

Formation

ULAS J0015+01 has been thought to either be a remnant of the Milky Way's formation or a merge with a different galaxy. Analysis of the surrounding environment does not favor the presence of a star within such a place of low density important for star formation. Another explanation was that this star was part of a population of stars that was stripped from their parent galaxy by the Milky Way. If it were originally part of the Milky Way, it would have been ejected at a high velocity of around 600 km/s. Another hypothesis was it is part of an unknown galaxy with low surface brightness, but that seems unlikely. No other stars have been discovered past ULAS J0015+01 or ULAS J0744+25, which almost completely gets rid of the unknown galaxy hypothesis.

References

{{2014 in space M-type giants Extragalactic stars Astronomical objects discovered in 2014