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