HUBBLE TELESCOPE REVEALS SWARM OF GLITTERING STARS IN NEARBY GALAXY

Phil Plait, Sally Heap and Eliot Malumuth

Deep in the heart of the Large Magellanic Cloud (LMC; a small companion galaxy to our own Milky Way) is a tremendous cloud of gas called the Tarantula Nebula. For about the past five million years, the Tarantula has been busily turning itself into stars. Very busily-- just in its center, the nebula has converted enough gas to form the mass equivalent of 15,000 Suns, and far more are being formed over the nebula as a whole. Because this is one of the largest and closest star forming regions known, it has long been subject to intense scrutiny by astronomers.

Ground-based image by Gary Bernstein and Megan Novicki (© the University of Michigan and Lucent).

In February 1996, Drs. Sally Heap and Eliot Malumuth at NASA's Goddard Space Flight Center pointed Hubble's Faint Object Spectrograph at the core of the cluster to investigate the properties of the very massive hot stars forming there. In parallel, they also switched on Hubble's Wide Field Planetary Camera 2 (WFPC2). The two instruments worked at the same time: while the spectrograph took data of the center of the nebula, WFPC2 took numerous deep, multi-color images of the outskirts. By taking observations far from the crowded center of the nebula, fainter stars were more easily detected since they were not overwhelmed by the much brighter stars near the core. In this way, we can find out more about how stars like our Sun are formed. Dr. Philip Plait (also from GSFC) analyzed the WFPC2 data.

The top image (in the panel of 3 images) is of the entire nebulosity complex and was taken by Gary Bernstein and Megan Novicki of the University of Michigan using a ground based telescope in Hawaii (we thank them for graciously allowing the image to be used here). The giant gas cloud spans the roughly 1500 light year field of this image. The bright center of the nebula can be seen in the center left of the image. The star which eventually blew up to become Supernova 1987A was born in this cloud, near the lower right hand side of the image.

This image is not as deep as the Hubble image (it had a much shorter exposure time) but it covers a much larger area of the sky. The white outline in the big picture represents the field of the next image, which is a zoom in on the ``suburbs'' of the Tarantula.

This smaller area of the nebula spans about 300 light years, and you can start to see some of the individual fainter stars and details of the gas. The outline of the Hubble image is shown in this image.

The field-of-view of the Wide Field and Planetary Camera 2 is overlaid on the ground-based image in the middle image and the "Starfield in the Large Magellanic Cloud" Hubble Heritage image is detailed in the bottom.

For the third image, three Hubble WFPC2 images have been combined to make a natural color picture of the region. (Editor's note: details about color assignments to black and white data can be found at technical information page and about specific assignments for this image in its fast facts table.)This picture represents the deepest multi-color images ever taken in the LMC; over 10,000 stars can be seen in the image, including stars as faint as 26th magnitude. The brightest stars in the image are 10,000 times fainter than can be seen with the unaided eye, and the faintest are 100 million times dimmer! At this distance, the Sun itself would be about 23rd magnitude, and would be lost in the wash of thousands of stars. In the image are also sheets of nebular gas which are shaped by their interaction with the light and winds from nearby stars. Also visible are dark patches of interstellar dust which block our view of the stars behind them. In the Hubble image, stars as close together as 0.2 light years can be distinguished from each other. That's 20 times closer than the Sun to its nearest stellar neighbor, Proxima Centauri!

Note the different colors of the stars. The brightest stars are giants, much larger than the Sun, which are hundreds or thousands of times brighter than the Sun. They are bluish white or red- the red giants are nearing the end of their short lives, and may end as supernovae, or exploding stars. Fainter stars come in all colors, most obviously blue or yellow, and some fainter reddish stars can also be seen. These stars are less massive and cooler than the Sun, shining with a ruddy glow.

By studying such deep images, we hope to learn more about what triggers star formation and why it produces the kinds of stars it does. Understanding stars is fundamental to understanding how our own Sun behaves, how it affects us on Earth and possibly even how other stars can form their own planets and solar systems.