Gemini Focuses on a Mid-sized Galactic Black Hole June 6, 2019

Light echo measured from the central black hole in a dwarf galaxy NGC 4395. The time delay between the continuum from the black hole’s accretion disk (blue light curve) and the hydrogen emission from orbiting gas clouds (red light curve) is measured as ~80 min., providing the light travel time from the black hole to the gas emission region. Credit for NGC 4395 image: Adam Block/Mount Lemmon SkyCenter/University of Arizona. Credit for accretion disk illustration: NASA/Chandra X-ray Observatory/M. Weiss.

An international team of researchers led by astronomer Jong-Hak Woo obtained deep spectroscopy from Gemini, combined with light echo measurements from multiple observatories, to confirm a black hole “missing link.”

A team led by astronomer Jong-Hak Woo of Seoul National University have found strong evidence for an elusive intermediate mass black hole at the core of a small (dwarf) galaxy. The groundbreaking work is published on June 10 on Nature Astronomy. The preprint is available here.

Astronomers have long debated the existence of intermediate mass black holes with masses between those of individual giant stars and the supermassive black holes found at the cores of larger galaxies. Supermassive black holes can have masses with millions, or even billions, of solar masses.

The team used light echoes, or light that bounces off material surrounding the galaxy’s nucleus, to make the determination. “We have measured the shortest delay time for any echo ever observed in the light coming from the material falling into a black hole at the center of a galaxy,” said Woo. “When we combine that with the deep spectroscopic observations from Gemini, our team determined that this black hole has a mass of about 10,000 times the mass of our Sun.”

According to Woo, the Gemini observations were critical in determining the velocity of gases swirling around the black hole. “These velocities, which are over 400 kilometers per second, when combined with our light echo measurements, provide a solid basis for estimating the mass of the galaxy’s central black hole,” adds Woo.

To determine the black hole’s mass, Woo and his team measured the velocity of gas clouds orbiting around the black hole (using the Gemini spectroscopic observations) and the distance of the gas clouds from the black hole (using the echo delay observations). Based on these two measurements (velocity and distance), the mass of the black hole can be calculated using the basic physics of Newton’s Laws.

The galaxy targeted by the team is a dwarf galaxy and goes by the designation NGC 4395. Careful observations of the varying intensity of the light emitted from the center of the galaxy confirmed that the additional “travel time” for the echoes of the emissions from gasses swirling around the black hole is on the order of 80 minutes. This sets critical limits on the size of the black hole’s influence and thus its mass.

A team led by astronomer Jong-Hak Woo of Seoul National University have found strong evidence for an elusive intermediate mass black hole at the core of a small (dwarf) galaxy. The groundbreaking work is published on June 10 on Nature Astronomy. The preprint is available here.

Astronomers have long debated the existence of intermediate mass black holes with masses between those of individual giant stars and the supermassive black holes found at the cores of larger galaxies. Supermassive black holes can have masses with millions, or even billions, of solar masses.

The team used light echoes, or light that bounces off material surrounding the galaxy’s nucleus, to make the determination. “We have measured the shortest delay time for any echo ever observed in the light coming from the material falling into a black hole at the center of a galaxy,” said Woo. “When we combine that with the deep spectroscopic observations from Gemini, our team determined that this black hole has a mass of about 10,000 times the mass of our Sun.”

According to Woo, the Gemini observations were critical in determining the velocity of gases swirling around the black hole. “These velocities, which are over 400 kilometers per second, when combined with our light echo measurements, provide a solid basis for estimating the mass of the galaxy’s central black hole,” adds Woo.

To determine the black hole’s mass, Woo and his team measured the velocity of gas clouds orbiting around the black hole (using the Gemini spectroscopic observations) and the distance of the gas clouds from the black hole (using the echo delay observations). Based on these two measurements (velocity and distance), the mass of the black hole can be calculated using the basic physics of Newton’s Laws.

The galaxy targeted by the team is a dwarf galaxy and goes by the designation NGC 4395. Careful observations of the varying intensity of the light emitted from the center of the galaxy confirmed that the additional “travel time” for the echoes of the emissions from gasses swirling around the black hole is on the order of 80 minutes. This sets critical limits on the size of the black hole’s influence and thus its mass.

At a distance of 14 million light years, the center of the dwarf galaxy NGC 4395 has been the subject of extensive studies in the past. The brightness of its nucleus signals the presence of an actively accreting black hole at its center but nailing down its mass has been difficult. “We believe we have nailed it this time,” said Woo.

“Korea joined Gemini as an international partner less than a year ago. Clearly, Dr Woo and his colleagues are already making great use of our flagship optical-infrared observatory to contribute to Gemini science advances,” said Chris Davis of the National Science Foundation (NSF).

In addition to the Gemini observations, which used the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North telescope on Hawaii’s Maunakea, multiple observatories provided the data used to measure the light echo delays. The light echo measurements utilized the MDM Hiltner 2.4-meter telescope, the 1-meter Lemmonsan Optical Astronomy Observatory (LOAO), and the 1-meter Mt. Laguna Observatory (MLO).

At a distance of 14 million light years, the center of the dwarf galaxy NGC 4395 has been the subject of extensive studies in the past. The brightness of its nucleus signals the presence of an actively accreting black hole at its center but nailing down its mass has been difficult. “We believe we have nailed it this time,” said Woo.

“Korea joined Gemini as an international partner less than a year ago. Clearly, Dr Woo and his colleagues are already making great use of our flagship optical-infrared observatory to contribute to Gemini science advances,” said Chris Davis of the National Science Foundation (NSF).

In addition to the Gemini observations, which used the Gemini Multi-Object Spectrograph (GMOS) on the Gemini North telescope on Hawaii’s Maunakea, multiple observatories provided the data used to measure the light echo delays. The light echo measurements utilized the MDM Hiltner 2.4-meter telescope, the 1-meter Lemmonsan Optical Astronomy Observatory (LOAO), and the 1-meter Mt. Laguna Observatory (MLO).

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Science Contact:

• Jong-Hak Woo
  Professor, Physics and Astronomy
  Seoul National University
  Email: woo@astro.snu.ac.kr
  Desk phone: +82-2-880-4231
  Cell Phone: +82-10-7125-4231

Media Contact:

• Peter Michaud
  Gemini Observatory, PIO Manager
  Email: pmichaud@gemini.edu
  Desk phone: 808-974-2510
  Cell phone: 808-936-6643

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The Search for Seeds of Black Holes

The galaxy NGC 4395 is shown here in infrared light, captured by NASA's Spitzer Space Telescope. Image credit: NASA/JPL-Caltech.  ›Full image and caption

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 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, form 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, Va. Satyapal is 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, Calif., 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, Calif., 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, Md. The science instrument was built by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was built by Ball Aerospace & Technologies Corp. in Boulder, Colo. 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.

More information on WISE and NEOWISE can be found online at: http://www.nasa.gov/wise, http://wise.astro.ucla.edu and http://jpl.nasa.gov/wise

Whitney Clavin 818-354-4673
Jet Propulsion Laboratory, Pasadena, Calif.
whitney.clavin@jpl.nasa.gov