NASA finds missing cosmic matter

Feb 03, 2005

Found: 7 percent of the mass of the universe. Missing since: 10 billion years ago.

Consider one more astronomical mystery solved. Scientists have located a sizeable chunk of the universe that seemed to be missing since back when the stars first formed. It’s floating in super-hot rivers of gas, invisible to the naked eye, surrounding galaxies like our own. And a completely different kind of mystery matter -- dark matter -- may have put it there. The results appear in the current issue of the journal Nature.

To make this latest discovery, astronomers at Ohio State University and their colleagues used NASA’s Chandra X-ray Observatory to take the highest-quality spectrum of its type ever made.

Though astronomers had previously detected the rivers of gas with X-ray telescopes, this is the first time that the gas has been studied in enough detail to calculate how much of it is out there. The amount of gas matches the amount of material that went missing 10 billion years ago, said Smita Mathur, associate professor of astronomy at Ohio State.

She and doctoral student Rik Williams did this work with astronomers at the Harvard-Smithsonian Center for Astrophysics (CfA), the University of California, Berkeley, the Instituto de Astronomia in Mexico, and the Massachusetts Institute of Technology. The lead author on the paper is Fabrizio Nicastro of CfA.

According to current theories, when the universe began, it contained a certain amount of normal matter, a cache of protons and neutrons that today make up all normal atoms -- “stuff” as we know it.

Astronomers can use optical telescopes to look back in time and see what happened to the normal atoms, called baryons. Around 10 billion years ago, when half of the baryons became stars and galaxies and lit up the sky, the other half just seemed to disappear.

This new study shows that the missing baryons are still out there, Mathur said, they’re just floating in gas that is too hot to see with an optical telescope.

The gas that surrounds our galaxy, for example, is 100 times hotter than the sun -- so hot that it shines in high-energy X-rays instead of lower-energy visible light.

In 2002, Mathur and her colleagues used Chandra’s X-ray telescope to gather the first evidence that the gas was made of baryons. The image they obtained was a spectrum, a measurement of the different wavelengths of X-rays emanating from the material. But to prove that there was enough material there to account for the all the missing baryons, they knew they needed to take a better spectrum with the telescope.

“Those first results were tantalizing, but not foolproof. The signal-to-noise ratio in the spectrum was just not good enough,” Mathur said.

They needed a bright light source to pump up the signal, one located on the other side of the gas as viewed from Earth, so that the light shined directly through the gas. They found their source in a quasar, located in the constellation Ursa Major -- the Big Dipper.

Astronomers believe that quasars are galaxies with very massive black holes in the center. The black holes in quasars don’t just suck material in, they also shoot material out in a high-speed jet. The jet glows brightly, and the result is an intense beam of light -- exactly what Mathur and her colleagues needed to take their picture.

The astronomers decided to use the light from Markarian 421, one of the brightest quasars known. On two days -- one in October 2002 and another in July 2003 -- when Markarian 421 was at its brightest and the beam of light was pointing right at Earth, Mathur’s team took two very high quality X-ray spectra of the intervening gas.

Judging by the high signal-to-noise ratio of the data, the astronomers believe that one of their images is the best X-ray spectrum ever taken.

That spectrum isn’t what most people would consider a pretty picture -- it’s really just a graph of energy levels of light that penetrated the gas -- but to Mathur it’s absolutely beautiful, because it proved definitively that there are enough baryons -- “normal” atoms -- out there to account for the missing mass.

“This is such a wonderful spectrum that there is just no doubt about it,” she said.

Once they had the new spectra, the astronomers were able to calculate the density of baryons in the gas, and confirmed that the amount of material matched the missing matter they were searching for.

As to how the missing baryons ended up where they are, Mathur suspects that they were drawn there by the gravity of a different kind of matter, known as dark matter. Astronomers know that some unseen material provides most of the gravity of the universe, though they disagree on what dark matter is actually made of.

If Mathur and her colleagues are right, then their finding supports a dramatic theory: that dark matter provides a kind of backbone to the universe, where the structure of normal matter like galaxies follows an underlying structure of dark matter.

This research was sponsored by NASA-Chandra grants and NASA’s Long-Term Space Astrophysics program.


Explore further: SDO captures images of two mid-level flares

add to favorites email to friend print save as pdf

Related Stories

Budget deal takes aim, but misses on climate plans

Dec 11, 2014

A congressional deal to finance the government chips away at some Obama administration energy and environmental programs, but leaves largely intact the president's plans on global warming—at least until Republicans take ...

The mystery of pulsar rarity at the center of our galaxy

Nov 06, 2014

The galactic center is a happening place, with lots of gas, dust, stars, and surprising binary stars orbiting a supermassive black hole about three million times the size of our sun. With so many stars, as ...

Studying the physics of galaxies

Nov 03, 2014

Assistant Professor of Astronomy Evan Kirby arrived on campus in August. Born and raised in New Orleans, Kirby earned his BS in 2004 from Stanford University; his undergraduate thesis involved trips to Pasadena ...

Scientific instruments of Rosetta's Philae lander

Sep 23, 2014

When traveling to far off lands, one packs carefully. What you carry must be comprehensive but not so much that it is a burden. And once you arrive, you must be prepared to do something extraordinary to make ...

Recommended for you

SDO captures images of two mid-level flares

Dec 19, 2014

The sun emitted a mid-level flare on Dec. 18, 2014, at 4:58 p.m. EST. NASA's Solar Dynamics Observatory, which watches the sun constantly, captured an image of the event. Solar flares are powerful bursts ...

Why is Venus so horrible?

Dec 19, 2014

Venus sucks. Seriously, it's the worst. The global temperature is as hot as an oven, the atmospheric pressure is 90 times Earth, and it rains sulfuric acid. Every part of the surface of Venus would kill you ...

Image: Christmas wrapping the Sentinel-3A antenna

Dec 19, 2014

The moment a team of technicians, gowned like hospital surgeons, wraps the Sentinel-3A radar altimeter in multilayer insulation to protect it from the temperature extremes found in Earth orbit.

Video: Flying over Becquerel

Dec 19, 2014

This latest release from the camera on ESA's Mars Express is a simulated flight over the Becquerel crater, showing large-scale deposits of sedimentary material.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.