NGC 5746: Detection of hot halo gets theory out of hot water

Feb 03, 2006
NGC 5746: Detection of hot halo gets theory out of hot water
Credit: X-ray: NASA/CXC/U. Copenhagen/K.Pedersen et al; Optical: Palomar DSS

Scientists using NASA's Chandra X-ray Observatory have detected an extensive halo of hot gas around a quiescent spiral galaxy. This discovery is evidence that galaxies like our Milky Way are still accumulating matter from the gradual inflow of intergalactic gas.

"What we are likely witnessing here is the ongoing galaxy formation process," said Kristian Pedersen of the University of Copenhagen, Denmark, and lead author of a report on the discovery.

Chandra observations show that the hot halo extends more than 60,000 light years on either side of the disk of the galaxy known as NGC 5746. The detection of such a large halo alleviates a long-standing problem for the theory of galaxy formation. Spiral galaxies are thought to form from enormous clouds of intergalactic gas that collapse to form giant, spinning disks of stars and gas.

One prediction of this theory is that large spiral galaxies should be immersed in halos of hot gas left over from the galaxy formation process. Hot gas has been detected around spiral galaxies in which vigorous star formation is ejecting matter from the galaxy, but until now hot halos due to infall of intergalactic matter have not been detected.

"Our observations solve the mystery of the missing hot halos around spiral galaxies," said Pedersen. "The halos exist, but are so faint that an extremely sensitive telescope such as Chandra is needed to detect them."

NGC 5746 is a massive spiral galaxy about a 100 million light years from Earth. Its disk of stars and gas is viewed almost edge-on. The galaxy shows no signs of unusual star formation, or energetic activity from its nuclear region, making it unlikely that the hot halo is produced by gas flowing out of the galaxy.

"We targeted NGC 5746 because we thought its distance and orientation would give us the best chance to detect a hot halo caused by the infall of intergalactic gas," said Jesper Rasmussen of the University of Birmingham, United Kingdom and a coauthor of the report. "What we found is in good agreement with computer simulations in which galaxies are built up gradually from the merger of smaller clouds of hot gas and dark matter."

The computer simulations were done by Jesper Sommer-Larsen (also a coauthor of the report) and collaborators at the University of Copenhagen. The paper describing these results will be published in the April issue of the journal New Astronomy. Other researchers on this project were Sune Toff, Yale University; Andrew Benson, University of Oxford, United Kingdom; and Richard Bower, University of Durham, United Kingdom.

Source: Chandra X-ray Center

Explore further: Lunar explorers will walk at higher speeds than thought

add to favorites email to friend print save as pdf

Related Stories

Evidence for supernovas near Earth

Aug 27, 2014

Once every 50 years, more or less, a massive star explodes somewhere in the Milky Way. The resulting blast is terrifyingly powerful, pumping out more energy in a split second than the sun emits in a million ...

A spectacular landscape of star formation

Aug 20, 2014

This image, captured by the Wide Field Imager at ESO's La Silla Observatory in Chile, shows two dramatic star formation regions in the Milky Way. The first, on the left, is dominated by the star cluster NGC ...

A possible signal from dark matter?

Aug 12, 2014

(Phys.org) —Galaxies are often found in groups or clusters, the largest known aggregations of matter and dark matter. The Milky Way, for example, is a member of the "Local Group" of about three dozen galaxies, ...

Evidence of a local hot bubble carved by a supernova

Jul 30, 2014

I spent this past weekend backpacking in Rocky Mountain National Park, where although the snow-swept peaks and the dangerously close wildlife were staggering, the night sky stood in triumph. Without a fire, ...

Recommended for you

Lunar explorers will walk at higher speeds than thought

11 hours ago

Anyone who has seen the movies of Neil Armstrong's first bounding steps on the moon couldn't fail to be intrigued by his unusual walking style. But, contrary to popular belief, the astronaut's peculiar walk ...

Space: The final frontier... open to the public

13 hours ago

Historically, spaceflight has been reserved for the very healthy. Astronauts are selected for their ability to meet the highest physical and psychological standards to prepare them for any unknown challenges. However, with ...

NASA releases IRIS footage of X-class flare (w/ Video)

13 hours ago

On Sept. 10, 2014, NASA's newest solar observatory, the Interface Region Imaging Spectrograph, or IRIS, mission joined other telescopes to witness an X-class flare – an example of one of the strongest solar flares—on ...

NASA's Maven spacecraft reaches Mars this weekend

13 hours ago

Mars, get ready for another visitor or two. This weekend, NASA's Maven spacecraft will reach the red planet following a 10-month journey spanning 442 million miles (711 million kilometers).

User comments : 0