Peering deep into the heart of our Milky Way galaxy, NASA's Hubble Space
Telescope reveals a rich tapestry of more than half a million stars. Except for
a few blue, foreground stars, the stars are part of the Milky Way's nuclear star
cluster, the most massive and densest star cluster in our galaxy. So packed with
stars, it is equivalent to having a million suns crammed into the volume space
between us and our closest stellar neighbor, Alpha Centauri. At the very hub of
our galaxy, this star cluster surrounds the Milky Way's central supermassive
black hole, which is about 4 million times the mass of our sun.
Astronomers used Hubble's infrared vision to pierce through the dust in the
disk of our galaxy that obscures the star cluster. In this image, scientists
translated the infrared light, which is invisible to human eyes, into colors
our eyes can see. The red stars are either embedded or shrouded by intervening
dust. Extremely dense clouds of gas and dust are seen in silhouette, appearing
dark against the bright background stars. These clouds are so thick that even
Hubble's infrared capability could not penetrate them.
Hubble's sharp vision allowed astronomers to measure the movements of the
stars over four years. Using this information, scientists were able to infer
important properties such as the mass and structure of the nuclear star cluster.
The motion of the stars may also offer a glimpse into how the star cluster was
formed - whether it was built up over time by globular star clusters that happen
to fall into the galaxy's center, or from gas spiraling in from the Milky Way's
disk to form stars at the core.
This picture, spanning 50 light-years across, is a mosaic stitched from nine
separate images from Hubble's Wide Field Camera 3. The center of the Milky Way
is located 27,000 light-years away. The "snowstorm" of stars in the image is
just the tip of the iceberg: Astronomers estimate that about 10 million stars
in this cluster are too faint to be captured in this image.
This image was created from archival data of the Milky Way Center from multiple science proposals led by Tuan Do and Andrea Ghez from UCLA. STScI Research and Instruments Analyst Varun Bajaj was instrumental in mosaicking the multiple pointings together and working on the color composite of the WFC3 data.
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Acknowledgment: T. Do and A. Ghez (UCLA), and V. Bajaj (STScI)