Smoking Galaxy Weaves Web Of 'Pollution' - And A Mystery

June 09, 1997

WINSTON-SALEM, N.C. -- Where there is smoke, there is fire. And when a galaxy smokes, supernovas are usually involved, or so astronomers thought.

But now, in a stunning picture that reveals a distant galaxy entangled in a vast web of dust clouds, astronomers are rethinking how galaxies "pollute" their surrounding halos, ejecting dark clouds thousands of light years in extent and collectively capable of enmeshing entire galaxies.

"It's a lot cloudier than we expected in to be," said Blair D. Savage, a University of Wisconsin-Madison astronomer who, with graduate student Christopher Howk, captured the image of the galaxy NGC 891 with the WIYN Telescope, a state-of-the-art telescope operated by a consortium of universities and the National Optical Astronomy Observatories (NOAO) atop Kitt Peak, Ariz. NOAO is an arm of the National Science Foundation (NSF).

Situated 30 million light years from Earth, NGC 891 is a spiral galaxy like the Milky Way, yet its orientation is such that from Earth its central plane can be viewed edge-on. Using the 3.5 meter WIYN Telescope, which has a wide field of view, the Wisconsin astronomers discovered a galaxy-enveloping network of dust clouds that seem to emanate from many regions of the galaxy disk.

"What we found," said Savage "was a highly polluted atmosphere of this galaxy. The hundreds of clouds are irregularly distributed and have a wide variety of shapes and extents" with some found as far as 5,000 light years above the galaxy's central disk.

The galactic dust clouds are composed mostly of hydrogen, helium and a very small, solid grain of carbon and silicate dust. Astronomers think the extensive clouds of dust that permeate the space between stars within galaxies is, literally, stardust, the ejected remains of stars that died long ago in peaceful and violent events known as supernovas.

It was long believed -- and it may still be the case -- that supernova events, heating galactic space to temperatures of a million degrees or more, propelled some dust in chimney-like fashion up into the outer reaches or halos of galaxies. But finding a massive network of dust clouds in the halo of the galaxy was a surprise, said Savage, because it was believed the fragile interstellar dust grains would be consumed by the hot gases produced in violent supernova explosions.

The discovery of networks of clouds interwoven throughout the galactic halo of NGC 891 suggests that the picture is more complicated, or that other, gentler kinds of processes may be at work, said Howk.

"If the ejection process was just supernova-driven, we might expect to see just a few galactic chimneys" where dust in hot, over-pressurized regions is funneled up from the plane of the galaxy, Howk said. In fact, in some places the dust clouds appear isolated, while in other places they connect with active regions of the galaxy in chimney- like structures.

One possible explanation for the widespread distribution of the dust clouds, said Savage, is that the dust is also carried high into the halo by the gentle pressure of starlight. A similar process involving the pressure of sunlight produces the beautiful tails of dust observed to extend from comets as they orbit the sun.

The existence of the clouds in the halo of NGC 891, at the least, provides astronomers with a completely new way of studying the flow of matter from the disks into the halos of spiral galaxies, said Savage.

The telescope used to make the discovery, known as WIYN, is one of a new generation of ground-based telescopes making important fundamental contributions to understanding space and the objects that populate it. WIYN is operated by a consortium of universities including the University of Wisconsin-Madison, Indiana and Yale Universities, and the National Optical Astronomical Observatories, an arm of the National Science Foundation charged with managing and operating the suite of telescopes situated on Kitt Peak.

Contact: Blair D. Savage
Or: Christopher Howk

Editor's note: Images of the NGC 891 galaxy are posted at There is an accompanying high-resolution (300 dpi) JPEG version of each image for use in print publications.)

University of Wisconsin-Madison

Related Astronomers Articles from Brightsurf:

Astronomers are bulging with data
For the first time, over 250 million stars in our galaxy's bulge have been surveyed in near-ultraviolet, optical, and near-infrared light, opening the door for astronomers to reexamine key questions about the Milky Way's formation and history.

Astronomers capture a pulsar 'powering up'
A Monash-University-led collaboration has, for the first time, observed the full, 12-day process of material spiralling into a distant neutron star, triggering an X-ray outburst thousands of times brighter than our Sun.

Astronomers discover new class of cosmic explosions
Analysis of two cosmic explosions indicates to astronomers that the pair, along with a puzzling blast from 2018, constitute a new type of event, with similarities to some supernovae and gamma-ray bursts, but also with significant differences.

Astronomers discover planet that never was
What was thought to be an exoplanet in a nearby star system likely never existed in the first place, according to University of Arizona astronomers.

Canadian astronomers determine Earth's fingerprint
Two McGill University astronomers have assembled a 'fingerprint' for Earth, which could be used to identify a planet beyond our Solar System capable of supporting life.

Astronomers help wage war on cancer
Techniques developed by astronomers could help in the fight against breast and skin cancer.

Astronomers make history in a split second
In a world first, an Australian-led international team of astronomers has determined the precise location of a powerful one-off burst of cosmic radio waves.

Astronomers witness galaxy megamerger
Using the Atacama Large Millimeter/submillimeter Array (ALMA), an international team of scientists has uncovered a startlingly dense concentration of 14 galaxies that are poised to merge, forming the core of what will eventually become a colossal galaxy cluster.

Astronomers discover a star that would not die
An international team of astronomers has made a bizarre discovery; a star that refuses to stop shining.

Astronomers spun up by galaxy-shape finding
For the first time astronomers have measured how a galaxy's spin affects its shape -- something scientists have tried to do for 90 years -- using a sample of 845 galaxies.

Read More: Astronomers News and Astronomers Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to