What Are Dwarf Galaxies Teaching Us About Black Holes?

Over the past decade, we have come to appreciate that essentially every normal galaxy, including our Milky Way, harbors a supermassive black hole at its center. These monsters play an important role in the evolution of galaxies and the appearance of the observable universe, but their origin is largely unknown.

The growth of supermassive black holes over cosmic history appears to be linked to the buildup of their host galaxies, with more massive galaxies generally harboring more massive black holes. Therefore, finding and studying the smallest “dwarf ” galaxies hosting supermassive black holes can provide clues to the origin of such behemoths.

Until recently, however, astronomers knew of very few dwarf galaxies with supermassive black holes. These enormous singularities were almost exclusively found in giant galaxies, and the very existence of supermassive black holes in dwarf galaxies was controversial. That line of thinking is changing now, thanks in part to a new study using data from the Sloan Digital Sky Survey that has revealed more than 100 dwarf galaxies hosting supermassive black holes.

The black holes are only a few hundred thousand times the Sun’s mass, which is tiny in comparison to the most massive black holes that weigh in at nearly 10 billion times the Sun’s mass.

While its only found signatures of “active” black holes in a tiny fraction of these dwarf galaxies, the search technique is only sensitive to the brightest and most actively feeding ones. So there are likely many more supermassive black holes hiding out in dwarf galaxies.

  The ongoing complementary studies using radio and X-ray observations are already starting to unveil these hidden black holes. Ultimately, searching for and studying supermassive black holes in dwarf galaxies will provide important clues to the puzzling question: How did supermassive black holes that reside in the center of nearly every full-sized galaxy get started in the first place?
 

 Although the spiral arms of the Milky Way harbor many impressive clouds of gas and dust, few rival the Lagoon Nebula (M8) in Sagittarius the Archer.

During the past few million years, the Lagoon has spawned thousands of stars as dense pockets of gas collapsed under their own weight.

The hottest of these suns excite the surrounding hydrogen atoms and cause them to glow with a characteristic reddish color. M8 spans approximately 100 lightyears and lies roughly 5,000 light-years from Earth.
Astronomers captured this image with the 2.6-meter VLT Survey Telescope on Cerro Paranal in northern.

Source: https://goo.gl/HWXajF.