New Data Helps Astronomers Piece Together the Evolution of Supermassive Black Holes

Scientists Piece Together the Evolution of Supermassive Black Holes

The galaxy NGC 4395 is shown here in infrared light, captured by NASA’s Spitzer Space Telescope. This dwarf galaxy is relatively small in comparison with our Milky Way galaxy, which is nearly 1,000 times more massive.
The galaxy is “bulgeless” because it lacks a large collection of stars at its center. Astronomers using NASA’s Wide-field Infrared Survey Explorer, or WISE, have found more evidence that bulgeless galaxies, contrary to previous theories, do harbor supermassive black holes at their center. In this image, an actively feeding supermassive black hole resides in the galaxy’s nucleus, as seen by the bright red source. The feeding supermassive black hole dominates the infrared light coming from the galaxy’s center. Credit: NASA/JPL-Caltech

Using data from NASA’s Wide-field Infrared Survey Explorer, astronomers are piecing together the evolution of supermassive black holes.

How do you grow a supermassive black hole that is a million to a billion times the mass of our sun? Astronomers do not know the answer, but a new study using data from NASA’s Wide-field Infrared Survey Explorer, or WISE, has turned up what might be the cosmic seeds from which a black hole will sprout. The results are helping scientists piece together the evolution of supermassive black holes — powerful objects that dominate the hearts of all galaxies.

Growing a black hole is not as easy as planting a seed in the soil and adding water. The massive objects are dense collections of matter that are literally bottomless pits; anything that falls in will never come out. They come in a range of sizes. The smallest, only a few times greater in mass than our sun, forms from exploding stars. The biggest of these dark beasts, billions of times the mass of our sun, grow together with their host galaxies over time, deep in the interiors. But how this process works is an ongoing mystery.

Researchers using WISE addressed this question by looking for black holes in smaller, “dwarf” galaxies. These galaxies have not undergone much change, so they are more pristine than their heavier counterparts. In some ways, they resemble the types of galaxies that might have existed when the universe was young, and thus they offer a glimpse into the nurseries of supermassive black holes.

In this new study, using data of the entire sky taken by WISE in infrared light, up to hundreds of dwarf galaxies have been discovered in which buried black holes may be lurking. Infrared light, the kind that WISE collects, can see through dust, unlike visible light, so it’s better able to find the dusty, hidden black holes. The researchers found that the dwarf galaxies’ black holes may be about 1,000 to 10,000 times the mass of our sun — larger than expected for these small galaxies.

“Our findings suggest the original seeds of supermassive black holes are quite massive themselves,” said Shobita Satyapal of George Mason University, Fairfax, Virginia. Satyapal is the lead author of a paper published in the March issue of Astrophysical Journal.

Daniel Stern, an astronomer specializing in black holes at NASA’s Jet Propulsion Laboratory, Pasadena, California, who was not a part of the new study, says the research demonstrates the power of an all-sky survey like WISE to find the rarest black holes. “Though it will take more research to confirm whether the dwarf galaxies are indeed dominated by actively feeding black holes, this is exactly what WISE was designed to do: find interesting objects that stand out from the pack.”

The new observations argue against one popular theory of black hole growth, which holds that the objects bulk up in size through galaxy collisions. When our universe was young, galaxies were more likely to crash into others and merge. It is possible the galaxies’ black holes merged too, accumulating more mass. In this scenario, supermassive black holes grow in size through a series of galaxy mergers.

The discovery of dwarf galaxy black holes that are bigger than expected suggests that galaxy mergers are not necessary to create big black holes. Dwarf galaxies don’t have a history of galactic smash-ups, and yet their black holes are already relatively big.

Instead, supermassive black holes might form very early in the history of the universe. Or, they might grow harmoniously with their host galaxies, feeding off surrounding gas.

“We still don’t know how the monstrous black holes that reside in galaxy centers formed,” said Satyapal. “But finding big black holes in tiny galaxies shows us that big black holes must somehow have been created in the early universe, before galaxies collided with other galaxies.”

Other authors of the study include: N.J. Secrest, W. McAlpine, and J.L. Rosenberg of George Mason University; S.L. Ellison of the University of Victoria, Canada; and J. Fischer of the Naval Research Laboratory, Washington.

WISE was put into hibernation upon completing its primary mission in 2011. In September 2013, it was reactivated, renamed NEOWISE, and assigned a new mission to assist NASA’s efforts to identify the population of potentially hazardous near-Earth objects. NEOWISE will also characterize previously known asteroids and comets to better understand their sizes and compositions.

NASA’s Jet Propulsion Laboratory, Pasadena, California, manages and operates the NEOWISE mission for NASA’s Science Mission Directorate. The WISE mission was selected competitively under NASA’s Explorers Program managed by the agency’s Goddard Space Flight Center in Greenbelt, Maryland. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colorado. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

Reference: “Discovery of a Population of Bulgeless Galaxies with Extremely Red Mid-IR Colors: Obscured AGN Activity in the Low Mass Regime?” by Shobita Satyapal, Nathan J. Secrest, William McAlpine, Sara L. Ellison, Jacqueline Fischer and Jessica L. Rosenberg, 12 March 2014, The Astrophysical Journal.
DOI: 10.1088/0004-637X/784/2/113
arXiv:1401.5483

 

Be the first to comment on "New Data Helps Astronomers Piece Together the Evolution of Supermassive Black Holes"

Leave a comment

Email address is optional. If provided, your email will not be published or shared.