Abstract
It is now well-established that a dark, compact object, very likely a massive black hole (MBH) of around four million solar masses is lurking at the centre of the Milky Way. While a consensus is emerging about the origin and growth of supermassive black holes (with masses larger than a billion solar masses), MBHs with smaller masses, such as the one in our galactic centre, remain understudied and enigmatic. The key to understanding these holes—how some of them grow by orders of magnitude in mass—lies in understanding the dynamics of the stars in the galactic neighbourhood. Stars interact with the central MBH primarily through their gradual inspiral due to the emission of gravitational radiation. Also stars produce gases which will subsequently be accreted by the MBH through collisions and disruptions brought about by the strong central tidal field. Such processes can contribute significantly to the mass of the MBH and progress in understanding them requires theoretical work in preparation for future gravitational radiation millihertz missions and X-ray observatories. In particular, a unique probe of these regions is the gravitational radiation that is emitted by some compact stars very close to the black holes and which could be surveyed by a millihertz gravitational-wave interferometer scrutinizing the range of masses fundamental to understanding the origin and growth of supermassive black holes. By extracting the information carried by the gravitational radiation, we can determine the mass and spin of the central MBH with unprecedented precision and we can determine how the holes “eat” stars that happen to be near them.
Highlights
We are back to a spherical system world, in which orbits such as those in the previous section do not exist
It is important to note that claims of detection of “intermediate-mass” black holes (IMBHs) at the centre of globular clusters raise the possibility that these correlations could extend to much smaller systems, see e.g., Gebhardt et al (2002), Gerssen et al (2002)
Of detection of “intermediate-mass” black holes (IMBHs, with masses ranging between 100 − 104 M ) at the centre of globular clusters Gebhardt et al (2002), Gerssen et al (2002) raise the possibility that these correlations extend to much smaller systems, but so far the strongest, not conclusive, observational support for the existence of IMBHs are ultra-luminous X-ray sources Miller and Colbert (2004), Kong et al (2010)
Summary
1 solar mass = 1.99 × 1030 kg Mass of super- or massive black hole 1 parsec ≈ 3.09 × 1016 m One million/billion years Active galactic nucleus Black hole Compact object (a white dwarf or a neutron star), or a stellarmass black hole. A collapsed star with a mass ∈ [1.4, 10] M in this work Dark compact object Dynamical friction Extreme mass ratio inspiral Galactic centre Graphics processing unit Gravitational wave/s Giant stars in the horizontal branch Hubble space telescope Intermediate-mass black hole (M ∈ [102, 105] M ) Initial mass function Intermediate mass ratio inspiral Laser interferometer space antenna Last stable orbit Massive black hole (M ≈ 106 M ) Monte carlo Milky Way Direct-summation N -body Neutron star Post-Newtonian Red giant Root mean square Super massive black hole (M > 106 M ) Signal-to-noise ratio Smoothed particle hydronamics Tidal disruption event Ultra-compact dwarf galaxy Redshift
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