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Even small galaxies have huge black holes. This is the excerpt from a recent study of so-called dwarf galaxies – galaxies so small and dark that astronomers know only the relatively close galaxies. In addition, these black holes are somewhat explosive – engines that drive strong gas and radiation jets and suppress the growth of galaxies.

"This is one of the things you hope to find, and it came with thunder," said Gabriela Canalizo, astronomer at the University of California, Riverside, leading the research team. She and her colleagues found dwarf galaxies with black holes that provided more energetic feedback than they expected. The research was submitted to The Astrophysical Journal.

Astrophysicists have long thought that the largest galaxies (like our own Milky Way) have a monopoly on active mammoth black holes, often lurking in the center of the galaxy. Astronomers find them either by detecting the hard curves of nearby stars or by intercepting the glow that occurs when gas and stars invade, forming a radiation-spitting "active galactic nucleus".

But the weakness and diminution of the dwarf galaxies make their black holes extremely hard to spot. While the Milky Way comprises a few hundred billion stars, dwarves usually only harbor millions. Since astronomers can only track a few stars and only few gas and dust propel active galactic cores, it was assumed that all black holes in dwarf galaxies live up to their name and are too dark to find them. "We believe these things are there," partly because some computer simulations predict this, said Jillian Bellovary, astrophysicist at the American Museum of Natural History. "But they are invisible."

Not anymore. Researchers began their search by searching the Sloan Digital Sky Survey, a huge map of the northern night sky collected over many years. They searched for two criteria 29 relatively close to dwarf galaxies. First, they looked for radiation in certain optical and infrared wavelengths that could not come from just stars ̵

1; possible signs of an active galactic nucleus. Second, they picked out disk-shaped galaxies with saucer-like edges facing us. It is easier to study the movement of gases in these galaxies than in galaxies seen from the flat side.

Then they used the Keck giant telescope in Hawaii for follow-up. Looking closer at the 29 galaxies in question, they found 13 that showed evidence that oxygen ions lacked two electrons – a tell-tale signal from an active galactic nucleus. They also found that the gas in these 13 galaxies emanates at speeds of up to 1,000 kilometers per second – fast enough that at least a portion of the gas overcomes the gravitational pull of the galaxy and erupts into the intergalactic space.

Change what we know about the growth of these galaxies. Galaxies grow as lumps of gas and form new stars. During this process, other stars die in supernova explosions, disrupting the star formation process and expelling gas from the galaxy.

"We thought the growth of dwarf galaxies is regulated by supernova explosions," said Mar Mezcua, an astronomer at the Space Sciences Institute in Barcelona. However, these massive black holes in the form of active galactic nuclei are far stronger growth inhibitors. "It could be that they are more massive galaxies," in which the growth is dominated by giant central black holes and active galactic nuclei, they said exist. Many astrophysicists, including Bellovary, believe that such supermassive black holes grow when entire galaxies collide and collide with their central black holes, forming larger ones. If dwarf galaxies host large black holes, collisions between these smaller galaxies can eventually lead to black holes of the supermassive type, which can have the mass of billions of suns.

Tests of this idea may need to wait for the European Space Agency's Laser Interferometer Space Antenna or LISA. It was designed to measure gravitational waves that emanate from smaller black holes found in dwarf galaxies today. The planned start is still 15 years away.

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