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Andromeda's twin peaks.


With dust obscuring the center of our own galaxy, astronomers Famous astronomers and astrophysicists include:

Directory: A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A
  • Marc Aaronson (USA, 1950 – 1987)
  • George Ogden Abell (USA, 1927 – 1983)
 sometimes turn for answers to Andromeda, the nearest galaxy similar to the Milky Way Milky Way, the galaxy of which the sun and solar system are a part, seen as a broad band of light arching across the night sky from horizon to horizon; if not blocked by the horizon, it would be seen as a circle around the entire sky. . The core of this spiral neighbor, researchers reason, should contain features resembling those at the heart of our galaxy.

But Andromeda may not fully merit its reputation as a Milky Way look-alike. Newly released images, taken in 1991 by the Hubble Space Telescope Hubble Space Telescope (HST), the first large optical orbiting observatory. Built from 1978 to 1990 at a cost of $1.5 billion, the HST (named for astronomer E. P. Hubble) was expected to provide the clearest view yet obtained of the universe. , suggest that Andromeda has two distinct clusters of stars at its core. The Milky Way has just one.

The brighter cluster, visible from Earth, was thought to lie at Andromeda's exact center. But Hubble has uncovered a second, dimmer dim·mer  
n.
1. A rheostat or other device used to vary the intensity of an electric light.

2.
a. A parking light on a motor vehicle.

b. A low beam.
 nucleus of stars at the true center of the galaxy. The brighter cluster is offset from the dimmer center by about 5 light-years, says Tod R. Lauer Tod R. Lauer is an associate astronomer on the research staff of the National Optical Astronomy Observatory. He was a member of the Hubble Space Telescope WFPC team. His research interests includes observational searches for massive black holes in the centers of galaxies, the  of the National Optical Astronomy Observatories The United States National Optical Astronomy Observatory (NOAO) consists of three observatories under one management structure:
  • Kitt Peak National Observatory
  • Cerro Tololo Inter-American Observatory
  • National Solar Observatory
 in Tucson, Ariz.

When lauer and his colleagues first examined the Hubble images, they were hoping to find an intense spike of light -- evidence supporting the notion that a black hole lurks at Andromeda's heart. Instead, they found two less intense peaks.

Other spiral galaxies A spiral galaxy is a type of galaxy characterized by a central bulge of old Population II stars surrounded by a rotating disc of younger Population I stars. Spiral galaxies

Designation Picture Classification Constellation Apparent Magnitude
 have double centers, but Andromeda's twin peaks are more difficult to explain, Lauer says.

The brighter cluster could represent the remnant of a smaller galaxy that collided with Andromeda and was swallowed up by it a billion or so years ago, he says. However, the black hole thought to lie at Andromeda's center would have torn apart the remanant core in just a few hundred thousands years. The remnant might have survived longer if it had its own black hole, but its gravity would likely have distorted the true center of Andromeda, and the images don't show this, he adds.

Alternatively, the two peaks might actually be part of the same star cluster star cluster, a group of stars near each other in space and resembling each other in certain characteristics that suggest a common origin for the group. Stars in the same cluster move at the same rate and in the same direction. . A thick ring of dust cutting across the galaxy's center could create the illusion of two separate peaks, Lauer notes. But this explanation also poses problems, he says. Dust grams of average size would scatter visible light, causing the galaxy to appear redder--brighter at longer wavelenghts. Alas, Hubble detected no such effect.

A ring of larger dust grains could create the twin-peak illusion without producing reddening. But the dominance of larger grains at Andromeda's core would pose another puzzle: Why and when were the more typical, finer dust grains destroyed?

For now, admits Lauer, the Hubble images "raise more questions than they answer."
COPYRIGHT 1993 Science Service, Inc.
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1993, Gale Group. All rights reserved. Gale Group is a Thomson Corporation Company.

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Title Annotation:possible second star cluster observed with the Hubble Telescope
Publication:Science News
Article Type:Brief Article
Date:Aug 7, 1993
Words:400
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