Printer Friendly
The Free Library
4,489,051 articles and books
Member login
User name  
Password 
 
Join us Forgot password?

Andromeda's twin peaks.


With dust obscuring the center of our own galaxy, astronomers sometimes turn for answers to Andromeda

Andromeda, in astronomy

Andromeda, in astronomy, northern constellation located to the NE of Pegasus and to the S of Cassiopeia. Its brightest star, Alpheratz (Alpha Andromedae), marks the northeast corner of the Great Square in Pegasus. The constellation also contains the bright stars Mirach (Beta Andromedae) and Almach (Gamma Andromedae) and the famous Great Nebula, or Andromeda Galaxy, the only galaxy visible to the naked eye in the Northern
, 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. Although its motion is not readily apparent, the entire galaxy is rotating about the Milky Way's center. Relative to the universe, the galaxy is moving at a speed of c.370 mi per sec (c.. 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, 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 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 of the National Optical Astronomy Observatories 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 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. Two types of clusters can be distinguished—open clusters, also called galactic clusters because of their wide distribution in our galaxy (the Milky Way), and globular clusters.. 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.

 Reader Opinion

Title:

Comment:



 

Article Details
Printer friendly Cite/link Email Feedback
Title Annotation:possible second star cluster observed with the Hubble Telescope
Publication:Science News
Article Type:Brief Article
Date:Aug 7, 1993
Words:400
Previous Article:Evolution in a test tube: harnessing Darwin's theory to design new molecules.
Next Article:Radio days: VLBA turns on. (Very Long Baseline Array radio telescope to begin operation)
Topics:



Related Articles
Hubble: first light with a second eye. (Hubble Space Telescope)
Studying one galaxy by looking at another. (Andromeda galaxy's core may mimic our own galaxy's core)
Hubble camera finds huge star clusters. (found in Arp 220 galaxy) (Brief Article)
The little bang; was our galactic backyard the scene of past violence?(Cover Story)
Probing the members of globular clusters. (cataclysmic variables in star clusters)(Brief Article)
Hubble spies a cluster's unruly past.(Brief Article)
Andromeda feasts on its satellite galaxies.(Brief Article)
Image reveals galaxy's violent past. (Starry View).(Andromdeda)
Andromeda's building blocks.(Astronomy)(Brief Article)
Andromeda gets bigger.(GALACTIC STUDIES)(Andromeda galaxy expanding )(Brief Article)

Terms of use | Copyright © 2008 Farlex, Inc. | Feedback | For webmasters | Submit articles