Milky Way’s Most Distant Stars Spotted

A simulated image demonstrates how small the Milky Way would look from the star ULAS J0744+25. Image courtesy Visualization Software: Uniview by SCISS Data: SOHO (ESA & NASA), John Bochanski (Haverford College), and Jackie Faherty (American Museum of Natural History and Carnegie Institute’s Department of Terrestrial Magnetism)

Like a boat floating in a vast, empty ocean, a newly discovered star now holds the record as the most distant one in our Milky Way galaxy.

Galaxies are islands of stars spread throughout space, essentially, separated by voids littered with relatively few stars. The newly spotted Milky Way star, dubbed ULAS J0015+01, is a distant red giant that resides a jaw-dropping 900,000 light-years away. The most remarkable thing about the star is that it is still within the gravitational grasp of our own galaxy.

It was spotted along with another cool stellar old-timer named ULAS J0744+25, which is some 775,000  light-years away, by a team led by John Bochanski of Haverford College in Haverford, Pennsylvania.

The two stars are more than 50 percent farther from the sun than any known star in the Milky Way, or about five times more distant than the Large Magellanic Cloud, a dwarf galaxy that circles our galaxy. In fact, the two stars lie about one third of the distance to the Andromeda galaxy, the Milky Way’s sister spiral in the Local Group of nearby galaxies.

“The distances to these two stars are almost too large to comprehend,” says Bochanski. “To put it in perspective, when the light from ULAS J0015+01 left the star, our early human ancestors were just starting to make fires here on Earth.”

The feeble light from both red giants were picked up by the UKIRT Infrared Deep Sky Survey and Sloan Digital Sky Survey.

It’s a pretty lonely place beyond the Milky Way’s halo. Only seven stars having been cataloged to date that lie beyond the 400,000 light-year halo of stars that cocoon our galaxy.

But beyond the extreme records, these distant stars interest astronomers because they call the Milky Way’s extended halo their home. As far-flung outliers from the galaxy, they may shed light on its origin and evolution. Current theories point to our galaxy colliding with many smaller dwarf galaxies in the distant past, resulting in small smatterings of stars thrown out into intergalactic space. Both ULAS J0744+25 and ULAS J0015+01 may in fact be all that is left over of one such ancient collision.

See for Yourself

Okay, so while these stars are only visible with world-class telescopes, what about the most distant star visible to the naked eye?

If we are talking in terms of the brightest, most distant star then that would be Deneb, the lead star in the summertime constellation Cygnus. Despite having an estimated average distance of 1,400 light-years away, Deneb shines as one of the brightest stars in the heavens.

This sky-chart shows the location of Deneb, the lead star in the constellation Cygnus. Credit: SkySafari
This sky chart shows the location of Deneb, the lead star in the constellation Cygnus. Credit: SkySafari

It is easy to find at this time of the year for those in the Northern Hemisphere, since it lies overhead during late nights and pins down one of the corners of the Summer Triangle stellar pattern.

But the record as the farthest star we can see with the naked eye would probably have to go to Rho Cassiopeiae—at an astounding 8,000 light-years from Earth. That is 472,000 trillion miles (760,000 trillion kilometers) away.

This skychart shows the constellation Cassiopeia in the northeast evening sky, home to Rho Cass - the most distant star the unaided human eye can see.  Credit: SkySfari
This sky chart shows the constellation Cassiopeia in the northeast evening sky, home to Rho Cass, the most distant star the unaided human eye can see. Credit: SkySfari

Shining at magnitude +4.5,  it is just visible as a very faint star from the countryside or darker suburbs. The star glints from within the W- or M-shaped (depending on season) constellation Cassiopeia, the Queen. It can be seen throughout the year from mid-northern latitude locations, always in the general vicinity of the North Star.

The reason we can actually see Rho Cass is because it is classified as a hypergiant star, one that has a diameter some 500 times wider than our own sun, which it outshines 10,000 times more brightly. Astronomers believe this makes for an explosive combination and so computer models are suggesting that this stellar monster may explode as a supernovae anytime.

So, try and catch it while you can.

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Changing Planet

Meet the Author
Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.