A newly discovered object in the galaxy NGC 2276 may prove to be an important
black hole that helps fill in the evolutionary story of these exotic objects, as described in our latest
press release. The main image in this graphic contains a composite image of NGC 2766 that includes
X-rays
from NASA's Chandra X-ray Observatory (pink) combined with optical data
from the Hubble Space Telescope and the Digitized Sky Survey (red,
green and blue). The inset is a zoom into the interesting source that
lies in one of the galaxy's spiral arms. This object, called NGC
2276-3c, is seen in radio waves (red) in observations from the European
Very Long Baseline Interferometry Network, or EVN.
Astronomers have combined the X-ray and radio data to determine that
NGC 2766-3c is likely an intermediate-mass black hole (IMBH). As the
name suggests, IMBHs are
black holes
that are larger than stellar-mass black holes that contain about five
to thirty times the mass of the Sun, but smaller than supermassive black
holes that are millions or even billions of solar masses. The
researchers estimated the mass of NGC 2766-3c using a well-known
relationship between how bright the source is in radio and X-rays, and
the mass of the black hole. The X-ray and radio brightness were based on
observations with Chandra and the EVN. They found that NGC 2276-3c
contains about 50,000 times the mass of the Sun.
IMBHs are interesting to astronomers because they may be the seeds
that eventually evolve into supermassive black holes. They also may be
strongly influencing their environment. This latest result on NGC
2276-3c suggests that it may be suppressing the formation of new stars
around it. The EVN radio data reveal an inner jet that extends about 6
light years from NGC 2276-3c. Additional observations by the NSF's Karl
Jansky Very Large Array (VLA) show large-scale radio emission extending
out to over 2,000 light years away from the source.
A region along the jet extending to about 1,000 light years away from
NGC 2766-3c is devoid of young stars. This might provide evidence that
the jet has cleared out a cavity in the gas, preventing new stars from
forming there. The VLA data also reveal a large population of stars at
the edge of the radio emission from the jet. This enhanced star
formation could take place either when the material swept out by the jet
collides with dust and gas in between the stars in NGC 2276, or when
triggered by the merger of NGC 2276 with a dwarf galaxy.
In a separate study, Chandra observations of this galaxy have also
been used to examine its rich population of ultraluminous X-ray sources
(ULXs). Sixteen X-ray sources are found in the deep Chandra dataset seen
in this composite image, and eight of these are ULXs including NGC
2276-3c. Chandra observations show that one apparent ULX observed by
ESA's XMM-Newton is actually five separate ULXs, including NGC 2276-3c.
This ULX study shows that about five to fifteen solar masses worth of
stars are forming each year in NGC 2276. This high rate of star
formation may have been triggered by a collision with a dwarf galaxy,
supporting the merger idea for the IMBH's origin.
The
study on NGC 2276-3c was conducted by Mar Mezcua
(previously in the Instituto de Astrofisica de Canarias and now at the
Harvard-Smithsonian Center for Astrophysics), Tim Roberts (University of
Durham, UK), Andrei Lobanov ( Max Planck Institute for Radio Astronomy,
Germany), and Andrew Sutton (University of Durham) and will appear in
the Monthly Notices of the Royal Astronomical Society (MNRAS). A
separate paper
on the ULX population in NGC 2276 will also appear in MNRAS and the
authors on that study are Anna Wolter (National Institute for
Astrophysics (INAF) in Milan, Italy), Paolo Esposito (INAF), Michela
Mapelli (INAF, Padova), Fabio Pizzolato (University of Milan, Italy),
and Emanuele Ripamonti (University of Padova, Italy).
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program for NASA's Science Mission Directorate in
Washington. The Smithsonian Astrophysical Observatory in Cambridge,
Massachusetts, controls Chandra's science and flight operations.
Fast Facts for NGC 2276:
Scale: Image is 4.5 arcmin across (about 140,000 light years)
Category: Normal Galaxies & Starburst Galaxies
Coordinates (J2000): RA 07h 27m 14.48s | Dec +85° 45' 16.20"
Constellation: Cepheus
Observation Date: 23 Jun 2004 and 24 May 2013
Observation Time: 19 hours 30 min.
Obs. ID: 4968, 15648
Instrument: ACIS
References: Mezcua, M et al, 2015, MNRAS (accepted); arXiv:1501.04897; Wolter, A. et al, 2015, MNRAS (accepted); arXiv:1501.01994
Color Code: X-ray (Pink); Optical (Red, Green, Blue); Inset: Radio (Red)
Distance Estimate: About 100 million light years
