University of Iowa researchers have found a giant star orbiting a medium-sized black hole - a discovery they hope proves the existence of a new class of black hole and explains how they evolve.
The discovery was made indirectly as researchers noticed the black hole's X-rays became brighter and dimmer every 62 days. This showed them how often the star orbited the hole.
"This, in turn, told us that the companion star has to be a giant star - a phase in the evolution of a star when it becomes extremely bloated," said Philip Kaaret, an associate professor in the university's physics and astronomy department.
Kaaret said the discovery may help confirm the existence of "medium-sized" black holes - with masses 100 to 10,000 times more than our sun. The new class of holes would be larger than black holes that are formed from a normal star's collapse and smaller than the black holes in the centers of galaxies.
The researchers used a special X-ray telescope to find the star in the nearby starburst galaxy M82. The star is about 1,000 times larger than the sun.
"The discovery also explains why this black hole is so bright in X-rays," Kaaret said. "It's because the black hole can pull gas directly off from the outer layers of the giant star."
Student Melanie Simet, a senior from Cedar Falls, is one of the researchers. The group will await validation by other X-ray telescopes.
"This first discovery proves our technique, and we hope to make more discoveries with new X-ray observations of other black holes," Kaaret said.