Astronomy Now Online

Top Stories

The very first stars

...thanks to a revolutionary new computer simulation created by astrophysicists from Japan and America, the very first instance that stars breathed light on the Universe have been mimicked...

read more

Titan's liquid lakes

...Cassini scientists have presented unrivalled evidence for the presence of ethane lakes on Saturn’s moon Titan, the first definitive example of liquid surface reservoirs on a planetary body other than the Earth...

read more

Phoenix tastes water on Mars

...after weeks of struggling to deliver a sample of icy soil to Phoenix’s onboard laboratory, the lander’s ovens have finally received their bounty and provided the first direct evidence for water on Mars...

read more

Spaceflight Now +

Subscribe to Spaceflight Now Plus for access to our extensive video collections!
How do I sign up?
Video archive

STS-120 day 2 highlights

Flight Day 2 of Discovery's mission focused on heat shield inspections. This movie shows the day's highlights.


STS-120 day 1 highlights

The highlights from shuttle Discovery's launch day are packaged into this movie.


STS-118: Highlights

The STS-118 crew, including Barbara Morgan, narrates its mission highlights film and answers questions in this post-flight presentation.

 Full presentation
 Mission film

STS-120: Rollout to pad

Space shuttle Discovery rolls out of the Vehicle Assembly Building and travels to launch pad 39A for its STS-120 mission.


Dawn leaves Earth

NASA's Dawn space probe launches aboard a Delta 2-Heavy rocket from Cape Canaveral to explore two worlds in the asteroid belt.

 Full coverage

Dawn: Launch preview

These briefings preview the launch and science objectives of NASA's Dawn asteroid orbiter.

 Launch | Science

Become a subscriber
More video

Cosmic ghost haunts

Galaxy Zoo

Posted: August 5, 2008

A volunteer in the Galaxy Zoo campaign has identified the most mysterious and unique object found yet amongst the menagerie of one million galaxies available for online classification by armchair astronomers across the globe: a cosmic ghost.

“This discovery really shows how citizen science has come of age in the Internet world,” says Professor Bill Keel of the University of Alabama, a team member.

Just like any other volunteer Galaxy Zoo astronomer, Hanny Van Arkel is an ordinary member of the public – a dutch school teacher – but has found a distinctly extraordinary object that some observers are calling a cosmic ghost, which sports a huge central hole over 16,000 light years across.

Henny's Voorwerp is the green blob of gas in the centre of this image, sporting a 16,000 light year diameter hole and believed to be a light echo from the bright, stormy centre of a distant galaxy that has since turned out its lights. Image: Dan Smith, Peter Herbert, Matt Jarvis & the ING.

The object has also been nicknamed ‘Hanny’s Voorwerp’ (Voorwerp is dutch for ‘object’) and has been awarded time on the Hubble Space Telescope for follow-up work at a later date. But for now, the Galaxy Zoo-keepers can only speculate as to the origins and nature of the eerie cosmic ghost that haunts the image of a relatively normal frame of galaxies.

"What we saw was really a mystery,” says Schawinski, co-founder of the Galaxy Zoo, “It could have been in our Solar System, or at the edge of the Universe." Even after telescopes around the world were trained on the mysterious object, the astronomers were none the wiser because the Voorwerp didn't appear to contain any stars. Instead, it was made entirely of 10,000 degree Celsius hot gas that could only be illuminated by something powerful lurking in the vicinity, and so the team turned to nearby galaxy IC 2497 for clues.

“We think that in the recent past the galaxy IC 2497 hosted an enormously bright quasar," says Schawinski. "Because of the vast scale of the galaxy and the Voorwerp, light from the past still lights up the nearby Voorwerp even though the quasar shut down sometime in the last 100,000 years, and the galaxy's black hole itself has gone quiet." Similar light echoes have been seen around supernovae that exploded decades or centuries ago, but Hanny’s Voorwerp could be the nearest example of such a luminous quasar, with the next nearest active quasar – 3C 273 – a massive 1.7 billion light years further away.

"It's amazing to think that this object has been sitting in the
archives for decades and that amateur volunteers can help by spotting things like this online," says Hanny van Arkel, discoverer of the ‘ghost’.

The Galaxy Zoo project was conceived by Schawinski and his colleague Chris Lintott at Oxford University as a means to classify millions of galaxies in a way that an automated classification system would not be able to achieve. The project has so far been an overwhelming success and during the last year, over 150,000 armchair astronomers from all over the world submitted around 50 million online classifications for a set of one million galaxies. The next stage of the Galaxy Zoo enterprise will focus on more unusual astronomical objects, and will perhaps even uncover more beautiful mysteries like Hanny’s Voorwerp.

Related Story

Galaxy Zoo’s special exhibition of merging galaxies read more