Hubble Space Telescope
September 14, 2013

Nearby Massive, Dense ‘Red Nugget’ Galaxies Located By Astronomers

redOrbit Staff & Wire Reports - Your Universe Online

Researchers from the Harvard-Smithsonian Center for Astrophysics (CfA) report that they have solved the mystery of why none of the unusually small galaxies known as “red nuggets” were seen nearby – they were essentially hiding in plain sight.

These “red nuggets,” so named because of their miniature size and the fact that they are densely packed with stars of that color, had only been observed in the distant, young universe, the study authors explain in the latest edition of The Astrophysical Journal Letters.

According to astronomers, these galaxies challenged existing theories of galaxy formation, but the lack of any nearby specimens caused scientists to wonder why they had disappeared over time. However, by reviewing databases from the Sloan Digital Sky Survey, CfA astronomer Ivana Damjanov and her colleagues discovered nearby “red nuggets.”

The galaxies were so small, the investigators said, that they appeared to be stars in photographs taken from ground-based telescopes. However, their spectra revealed their true nature. Damjanov compared the search for “red nuggets” to panning for gold in a riverbed, having to wash away the extraneous material to uncover valuable data.

“By sifting through the Sloan data, the team dug up more than 600 ‘red nugget’ candidates. They are located at distances of 2.5 to 5.7 billion light-years from Earth,” the CfA reported in a statement Friday.

Damjanov’s team then turned to the Hubble Space Telescope database to locate photos of regions of the sky where those candidates were located. They located images of nine targets, confirming that they are just as compact as more distant “red nuggets” – with some of these compact, massive galaxies weighing up to 10 times more than the Milky Way while being just one-tenth the size.

“We think there are more of these red nuggets, or compact galaxies, hidden in the universe, waiting to be discovered,” added co-author Ho Seong Hwang of the Smithsonian Astrophysical Observatory. Damjanov and Hwang were joined by co-authors Igor Chilingarian of the Sternberg Astronomical Institute and Margaret Geller of the Smithsonian Astrophysical Observatory.

The researchers now plan to use the Hubble in order to investigate more of these massive, compact “red nugget” galaxies, hoping to determine whether they are located near other galaxies or as part of the intergalactic void. They also hope to discern the internal structures of the galaxies, which some believe could essentially become the “seeds” for the larger elliptical galaxies that are commonly seen today.

Image 2 (below): These images highlight the most massive of the newly discovered compact galaxies known as "red nuggets." The photo at left from the Sloan Digital Sky Survey shows that the galaxy is so small it appears starlike. The higher resolution photo at right from the Hubble Space Telescope reveals the object's true, extended shape. Credit: SDSS (left), NASA (right)