Hubble's In-Depth Look at Galaxy's Halo

NASA's Hubble Space Telescope has allowed astronomers to get a more in-depth look of an outer galaxy's halo of stars than ever before, thanks to new research.

Researchers probed the outskirts of the elliptical galaxy Centaurus A, and found that there's more to this stunning world than first meets the eye. Its halo extends much further from the galaxy's center than expected and the stars within this halo seem to be surprisingly rich in heavy elements.

The studied halo of stars is actually a swirling pairs of "arms" or elliptical fuzz, and an essential component of any galaxy. The halo of our own galaxy, the Milky Way, preserves signatures of both its formation and evolution. Yet, we know very little about haloes of galaxies other than our own because they are faint and spread out, making them difficult to study.

Now, using the Hubble Space Telescope - operated by NASA and the European Space Agency (ESA) - a team of astronomers has taken the most in-depth look at the giant Centaurus A galaxy, also called NGC 5128.

They have found that its halo spreads far further into space than expected and does so in an unexpected way.

"Tracing this much of a galaxy's halo gives us surprising insights into a galaxy's formation, evolution, and composition," lead author Marina Rejkuba of the European Southern Observatory in Garching, Germany, said in a statement. "We found more stars scattered in one direction than the other, giving the halo a lopsided shape - which we hadn't expected!"

Alongside this welcomed surprise, the Hubble team also discovered that Centaurus A is composed of the heavy elements hydrogen and helium even at the outermost locations explored.

The Milky Way, in comparison, has only small quantities of heavy elements, representing the way that galaxies first formed and evolved - slowly pulling in numerous small satellite galaxies and taking on their stars. The presence of heavy element's in the remote locations of Centaurus are significant in that they suggest it at one point merged with a larger spiral galaxy.

"These kinds of observations are fundamentally important to understanding the galaxies in the Universe around us," Rejkuba added.

These results were published online in Astrophysical Journal on July 22.