Most 'outrageously luminous' galaxies ever discovered

 Astronomers have observed the most luminous galaxies ever seen in the universe - objects so bright that the researchers have taken to calling them 'outrageously luminous'.

Researchers at University of Massachusetts Amherst in the US said that established descriptors such as "ultra- and hyper-luminous" used to describe previously brightest known galaxies do not even come close to describing the newly discovered objects.

"We've taken to calling them 'outrageously luminous' among ourselves, because there is no scientific term to apply," said undergraduate student Kevin Harrington, study's lead author.

Researchers used the 50-metre diameter Large Millimetre Telescope (LMT), the largest, most sensitive single-aperture instrument in the world for studying star formation.

It is located on the summit of Sierra Negra, a 15,000-foot extinct volcano in the central state of Puebla, a companion peak to Mexico's highest mountain.

Researchers also used the latest generation of satellite telescope and a cosmology experiment on the NASA/ESA collaboration Planck satellite that detects the glow of the 'Big Bang' and microwave background for this work.

They estimate that the newly observed galaxies they identified are about 10 billion years old and were formed only about 4 billion years after the Big Bang.

Harrington said that in categorising luminous sources, astronomers call an infrared galaxy "ultra-luminous" when it has a rating of about 1 trillion solar luminosities, and that rises to about 10 trillion solar luminosities at the "hyper-luminous" level.

Beyond that, for the 100 trillion solar luminosities range of the new objects, "we don't even have a name," he said.

"The galaxies we found were not predicted by theory to exist; they're too big and too bright, so no one really looked for them before," said Professor Min Yun from the University of Massachusetts Amherst.

The newly observed galaxies are not as large as they appear, the researchers said.
Follow-up studies suggest that their extreme brightness arises from a phenomenon called gravitational lensing that magnifies light passing near massive objects, as predicted by Einstein's general relativity.

As a result, from Earth they look about 10 times brighter than they really are.
Gravitational lensing of a distant galaxy by another galaxy is quite rare, said Yun, so finding as many as eight potential lensed objects as part of this research "is another potentially important discovery."

The research was published in the journal Monthly Notices of the Royal Astronomical Society.