Astronomers at the University of Massachusetts Amherst (UMass Amherst) announced that they have observed the most luminous galaxies that were ever seen in our universe. In fact, the galaxies are so bright that they cannot be described by previous descriptors like “ultra” and “hyper-luminous.” According to the researchers, those terms are inadequate, as they have previously been used to describe the luminosity of galaxies that are not nearly as bright as the ones the researchers just observed.
“We’ve taken to calling them ‘outrageously luminous’ among ourselves, because there is no scientific term to apply,” Kevin Harrington, the lead author and undergraduate researcher, said in a press release.
The project takes place in Professor Min Yun’s research group, which implements a Large Millimeter Telescope (LMT), which is 50 meters in diameter. This is the largest, most sensitive single-aperture instrument in the world that is specifically designed to observe star formation. UMass Amherst and Mexico’s Instituto Nacional de Astrofísica, Óptica y Electrónica collaborate and jointly operate the telescope, which is located on Sierra Negra. Sierra Negra is a 15,000-foot extinct volcano in Puebla, near Mexico’s highest peak.
Yun’s group reports that the newly observed galaxies are about 10 billion years old and were formed about four billion years after the Big Bang. Harrington said that when organizing and categorizing luminous galaxies, astronomers say an infrared galaxy is “ultra-luminous” when it has a rating of about 1 trillion solar luminosities. “Hyper-luminous” is used to describe galaxies at 10 trillion solar luminosities. The recently observed galaxies were measured to be 100 trillion solar luminosities.
Theoretically, these galaxies are not supposed to exist, because they are too big and too bright. Thus no one before this group of researchers has even thought to search for them. Discovering them helps the researchers estimate how much material preceded them, between the time of the Big Bang and their formation.
Follow-up studies suggest that the galaxies may not be as big as they initially appeared, as their extreme brightness is a result of gravitational lensing. This phenomenon, which was predicted by Einstein’s theory of general relativity, occurs when matter bends the path of light as it travels through space. Gravitational lensing of a distant galaxy itself is quite rare, so these discoveries were of interest to the researchers for multiple reasons.
“Finding lensed sources this bright is as rare as finding the hole in the needle in the haystack,” Harrington said.
The group conducted analyses that showed that the galaxies’ brightness is most likely due to the fast rate of star formation in those galaxies. While the Milky Way produces a few stars every year, this galaxy punches out a solar mass, or a collection of matter whose mass is equivalent to that of the
While the Milky Way produces a few stars every year, this galaxy punches out a solar mass, or a collection of matter whose mass is equivalent to that of the sun, about every hour.
Further research will be done to see how old these galaxies are and how much gas they must contain in order to sustain such extreme luminosities. Harrington, specifically, hopes to graduate this year and pursue doctoral work at Germany’s Max Planck Institute for Astronomy and the University of Bonn to continue his research on galaxy evolution.