100 million years and still going. A team of astronomers that includes Elizabeth Blanton, a CAS assistant professor of astronomy, has detected and measured the most powerful outburst known in the universe. Using data from NASA’s Chandra X-ray Observatory, it was discovered in a distant cluster of galaxies and is associated with what the researchers describe as a voracious supermassive black hole.

Chandra images reveal two cavities in the X-ray emission from the galaxy cluster, each 650,000 light-years across, that appear to have been created by jets of energy emitted from the black hole, an object a billion times more massive than our sun. Each cavity is filled with extremely high-energy electrons that emit the radio waves that were detected by the National Radio Astronomy Observatory’s Very Large Array, one of the world’s premier astronomical observatories, in Socorro, N.M.

Although black holes swallow energy, and this one is characterized by the researchers as voracious, they also violently eject powerful jets of high-energy particles. By calculating the density, temperature, and pressure of the X-ray-emitting hot gas surrounding the cavities created by the jets, the researchers were able to estimate how much energy was ejected to create the cavities. Using the standard estimate that about 10 percent of the gravitational energy of a black hole is used to launch the jets, they then estimated how much the black hole had swallowed: the mass of almost 300 million suns — a staggering figure.

According to the researchers, this outburst has been pushing gas away from the black hole at supersonic speeds for more than 100 million years. They estimate that the mass of the displaced gas is more than the mass of all the stars in the Milky Way.

The continuing activity of the black hole, say the scientists, may be preventing the formation of new stars, a process that depends on the cooling and coalescing of gas in a galaxy.

Blanton’s collaborators on the project are lead author Brian McNamara of Ohio University in Athens, Ohio, Paul Nulsen of the Harvard-Smithsonian Center for Astrophysics, and colleagues at the MIT Center for Space Research, the National Radio Astronomy Observatory in Socorro, and the astronomy department at the University of Virginia in Charlottesville.

The research was published in the January 6, 2005, edition of the journal Nature. Images of the eruption can be seen at http://chandra.harvard.edu/photo/2005/ms0735.

Discriminating odors. Animals can detect different classes of odors — identifying them in categories such as sweet or spicy, putrid or fresh — an ability scientists call clustering. They can also differentiate between similar but different odors in the same class, rose and lilac, for instance, or apple pie and curry, a process known as fine discrimination. Ehud Sivan, a research associate at the Center for BioDynamics (CBD), and Nancy Kopell, a CAS mathematics professor and CBD codirector, have been investigating how neurons in the sensory organs and in the brain operate to produce these different abilities to identify smells.

Working with data from locusts and fruit flies and using computational simulations of how the insects’ brains react to odor, their experiments have demonstrated that two different areas of the brain, the lateral horn and the mushroom body, and two related and parallel processes are involved in clustering and fine discrimination among odors.

Both processes begin with a network of nerve cells in the antennal lobe of the insect’s brain that fires when stimulated by an odor. These include excitatory projection neurons and inhibitory local neurons that fire in a synchronized pattern. In insects, oscillations generated by this synchronized activity have been shown to be important in fine discrimination, but not in clustering of odors.

Sivan’s and Kopell’s simulations organize the projection neurons into functional subsets, or groups. Kenyon cells, neurons located in the mushroom body, are each connected to a unique pattern of projection neurons within the functional subset. All projection neurons in the functional subset are also connected to a single neuron in the lateral horn.

When any combination of projection neurons in the functional subset is stimulated by an odor, the associated neuron in the lateral horn is stimulated, and an awareness of a particular class of odors is produced. This awareness does not depend on the exact pattern of projection neurons stimulated.

Fine discrimination, however, does depend on a particular pattern of stimulation of the projection neurons in the subset to produce a corresponding pattern of Kenyon cells that alerts the insect brain to a particular odor. The researchers demonstrated that this fine discrimination occurs only in the presence of oscillations.

This work was published in the December 21, 2004, issue of the Proceedings of the National Academy of Sciences.