domingo, 16 de octubre de 2011

A One-of-a-Kind Exceptional Galaxy? M85 May Not Harbor a Supermassive Balck Hole an Its Core


The prevalence of these black holes at the centers of galaxies is well established and commonly referred to as active galactic nuclei central engines. This tight correlation of black hole masses with host galaxy properties strongly suggests an underlying link between galaxy and black hole evolution. The black hole mass has also been found to be correlated with the stellar spheroid’s mass.
A recent study by astronomers from the University of Michigan appears to have found an exception: The well known M85. the team used the spectrograph on board the Hubble Space Telescope to examine the pull the central object had on stars in the nearby vicinity.

Current theoretical work addressing these scaling relations focuses on feedback from outflows that are powered by accretion onto the central black hole. Thus the consequences of black hole growth plays a role in regulating star formation in the galaxy However, astronomers do not have a complete understanding of the physics involved, and the pursuit of black hole masses remains important.

NGC 4382 lies in a narrow range in velocity dispersion, chosen because galaxies in this range may have either core or power-law surface brightness profiles. Ground-based velocity information was obtained from archival data using Spectrographic Areal Unit for Research on Optical Nebulae (SAURON) an integral-field spectrograph unit mounted on the William Herschel Telescope in La Palma. As the SAURON instrument and observations were designed to measure and characterize the internal kinematics.

In their study published in August in ArXix, Is there a black hole in NGC 4382, the team presented HST STIS observations of M85 and axisymmetric models of the galaxy to determine mass-to-light ration and central black hole mass. HST images show the nucleus to be double, suggesting the presence of a nuclear eccentric stellar disk similar to the Tremaine disk in Bodes Galaxy, M31, which has an active galactic nucleus harboring a supermassive black hole. Their conclusion was supported by the HST velocity dispersion profile. Despite evidence of a recent merger, they concluded that the inferred low black hole mass may explain the lack of nuclear activity.

The team did not discover a shift that would be indicative of a black hole with a mass expected for a galaxy of M85's size. Using an indirect method of determining the CMBH mass by looking at the the amount of overall light from the galaxy, which is generally correlated with black hole mass, indicated that M85 should contain a black hole of 300 million to 2 billion solar masses. But the study indicates that if M85 contains a central black hole, the upper limit for the black hole would be around 65 million solar masses.

An earlier 2009 study led by Alessandro Capetti from Osservatorio Astronoimco di Torino in Italy, also searched M85 for signs of radio emission from the black hole region, but was unable to detect any significant radio waves from the core which, if M85 had a significant black hole, should be present.

If more examples like M85 are found to be are more common that previously thought, astronomers may be forced to re-examine the current accepted belief all galaxies harbor massive black holes at their core.

Image credit:

Source: The Daily Galaxy

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