There's been something tugging at the Milky Way Galaxy, subtly pulling it one way while the universe's expansion should be pulling it the other. Scientists haven't been quite sure just what it was, but now there's a little bit more of a hint. Or a few dozen of them.
This "tug" is known in astronomical circles as the Great Attractor. It pulls not only at our galaxy, but at others nearby. Originally discovered in the 1970s and 1980s, it's puzzled astronomers for years.
Now, a group of astronomers has discovered a partial explanation: a treasure trove of galaxies, all within about 250 million light years of us. The results were published today in the Astrophysical Journal.
"The results implied motions of huge volumes towards an area in the sky where no mass in the form of galaxies could be recognised in the sky," co-author Renée C. Kraan-Korteweg, chair of the astronomy department at the University of Cape Town, said in an email. "This caused quite some consternation. Where was that mass, and what was it—and even if we could discover it, it pushed current acceptable cosmological models to the limits."
There's still work to do. After all, this is a piece of the great attractor, but not the whole story
The survey was able to peer behind the dust of the Milky Way using new radio astronomy techniques. The Parkes Observatory in Australia had upgraded hardware that finally had the sensitivity needed to find these new galaxies, some of which are dwarf companions to previously known galaxies.
"(The observations were possible) mainly (because of) the sensitivity and wide field of view of the multibeam receiver on the Parkes telescope," lead author Lister Staveley-Smith, director of the International Centre for Radio Astronomy Research (ICRAR), said in an email. "Both meant that we could 'blindly' survey the sky for previously unseen galaxies."
Staveley-Smith says the galaxies are normal galaxies, but they hint at larger structures that were previously unknown in that region. In addition, a series of very small galaxies were found in the "local void," an area that spans light years in which there are few clusters of galaxies.
Included in the results were at least a handful of very interesting galaxies. In particular, Kraan-Korteweg points toward a galaxy known as HIZOA J0836-43. While it's a nearby galaxy, it has a great amount of star-forming matter and acts more like a galaxy from the early universe than the middle-aged galaxies in our region of the universe.
"It was interesting because the galaxy had lots of gas and was star-forming quite intensively in its center," she said. "Something only seen in galaxies further back in time (at very high redshift, hence much earlier Universe)."
There's still work to do. After all, this is a piece of the great attractor, but not the whole story.
"The new galaxies help account for the tug, but do not fully explain it," Staveley-Smith said. "There must be other large concentrations of mass at larger distances, beyond our sensitivity limit."
Thus, the work continues on.
"What still needs to be investigated, calculated in more concrete detail is how much mass is there really (we can use the detected galaxies as mass tracers for that) and do the calculations," Kraan-Korteweg said.