astrophysical black holes - institute for research in...

Topical meeting on black holes

Astrophysical black holes

Habib KhosroshahiSchool of Astronomy, IPM

Friday, 6 December 13

What is an astrophysical black hole?

Types of black holes in astrophysics

How do we observe black holes?

Impact of black holes on astrophysical objects

Black holes; Exotic and mysterious


There are three types of black holes:

mathematical black holesphysical black holes astrophysical black holescosmological black holes

An astrophysical black hole is an object in which the mass is distributed within its event horizon and formed through astrophysical processes in the physical Universe.

What is a black hole?

See reviews by: Narayan 2005, Zhang 2010


There are three types of black holes:

mathematical black holesphysical black holes astrophysical black holescosmological black holes

An astrophysical black hole is an object in which the mass is distributed within its event horizon and formed through astrophysical processes in the physical Universe.

What is a black hole?

event horizon

Initial collapse Collapse continues BH forms Math BH

See reviews by: Narayan 2005, Zhang 2010


Black hole formation

Black holes form via gravitational collapse. Heavy stars can end up as a black holes a part of their internal evolution.

A lower limit for the BH mass?Physically there is no limit!

There is an astrophysical limit!

The key to black hole formation is the density

- Stellar

- Primordial (SEE THE NEXT PRESENTATION)


Black hole formationGravitational collapse occurs when the object's gravity overcomes its internal pressure.

- Not enough fuel

- Mass infall from surrounding objects (such that it does not rise the core temperature)

Remnant mass 3 to 4 solar masses. But the original star mass should be at least 12 solar mass!

This mechanism will produce STELLAR MASS black holes. No stellar process can produce BH mass < 3.0 solar masses. If found it

may be of primordial origin. What is the difference between a highly compact object and a black hole?

Is there an upper limit for the BH mass?http://essayweb.net/astronomy/blackhole.shtml


https://en.wikipedia.org/wiki/Pressure

https://en.wikipedia.org/wiki/Pressure

http://essayweb.net/astronomy/blackhole.shtml


Black hole formationGravitational collapse occurs when the object's gravity overcomes its internal pressure.

- Not enough fuel

- Mass infall from surrounding objects (such that it does not rise the core temperature)

Remnant mass 3 to 4 solar masses. But the original star mass should be at least 12 solar mass!

This mechanism will produce STELLAR MASS black holes. No stellar process can produce BH mass < 3.0 solar masses. If found it

may be of primordial origin. What is the difference between a highly compact object and a black hole?

Is there an upper limit for the BH mass?http://essayweb.net/astronomy/blackhole.shtml




Black hole associatesThe accretion disk

An accretion disk is matter that is drawn to the black hole. In rotating black holes and/or ones with a magnetic field, the matter forms a disk due to the mechanical forces present. In a Schwarzschild black hole, the matter would be drawn in equally from all directions, and thus would form an omni-directional accretion cloud rather than disk. Accretion disks can be heated due to internal friction to temperatures as high as 3 billion K.

The Jet

Jets form in Kerr black holes that have an accretion disk. The matter is funnelled into a disk-shaped torus by the hole's spin and magnetic fields, but in the very narrow regions over the black hole's poles, matter can be energised to extremely high temperatures and speeds, escaping the black hole in the form of high-speed jets.


Observations of black holes

Isolated Black Holes:

Isolated black holes, the result of the collapse of a single massive star, are too small to be detected with any telescope today. There are probably millions of black holes in the Milky Way, weighing between 3 and 30 solar masses.

• They follow a total of 6 long-duration microlensing events with HST, to derive the

masses of the lenses.

• This program will potentially provide the first clues on the frequency of isolated BHs in the

Galaxy.

http://smc2011.physics.unisa.it/talks/sahu.pdf




Observations of isolated black holes

No X-ray events associated with the position of MACHO-96-BLG-5Friday, 6 December 13

Observations of black holes

Black holes in binary systems:

If the black hole is in a binary star system, orbiting with a normal star, if the orbit is small enough the normal star will evolve off the Main Sequence and expand in size to a red giant until it fills its Roche Lobe. At this point it will begin to spill over, dumping gas into the Roche lobe of the black hole. As the gas falls toward the black hole, it swirls into a rapidly rotating accretion disk around the black hole, and as the gas spirals in it will heat up and emit high energy X-rays. The inner part of the disk heats up to 107 - 108 K, hot enough to create X-rays. Most come from well beyond the event horizon of the black hole. The radiation might still be emitted by the gas after it falls within the event horizon, but we will never see it.

An artist's impression of the HDE 226868︲Cygnus X-1 binary system.ESA/Hubble illustration. (1971-1974)


http://astronomy.nmsu.edu/geas/lectures/lecture26/pics/GRB.mov

http://astronomy.nmsu.edu/geas/lectures/lecture26/pics/GRB.mov

Observations of black holesBinary black holes

If two galaxies merge, their central black holes will merge too. Super massive black hole binaries are believed to form during galaxy mergers. Some likely candidates for binary black holes are galaxies with double cores still far apart. An example double nucleus is NGC 6240.

Much closer black hole binaries are likely in single core galaxies with double emission lines. Examples include SDSS J104807.74+005543.5.

Two black holes in the NGC 6240 galaxy. NASA/CXC/MPE

Binary Black Hole in 3C 75, NGC 1128


http://en.wikipedia.org/wiki/Galaxy_merger

http://en.wikipedia.org/wiki/Galaxy_merger

http://en.wikipedia.org/wiki/NGC_6240

http://en.wikipedia.org/wiki/NGC_6240

http://en.wikipedia.org/w/index.php?title=SDSS_J104807.74%2B005543.5&action=edit&redlink=1




Black hole mass

M33 X-7

Most massive stellar black hole known to date

15.7 solar mass

GRO J0422+32

Least massive stellar black hole known to date

3.5 to 5 solar mass

Stellar black hole mass range 10-100 solar masses

M33 X-7


The gap; real or a bias?

Belczynski, 2011

Study of black holes help us understand stellar evolution and SNe mechanisms.

Ivan Baldry


Supper massive black holes

Elliptical Galaxy: Visible and X-ray Views

The elliptical galaxy M87 also houses a monster in its middle: the most massive black hole yet observed in

our universe.

NASA / CXC / M. Forman, et al.Palomar Observatory, Digitized Sky Survey

Centaurus A is a nearby galaxy that is thought to be the result of a merger of two smaller galaxies. What’s behind the dust?

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Galaxy - black hole connection: co-evolution or just good friends?

A major piece of evidence in favor of co-evolution is the MBH − σ relation;

Since the gravitational sphere of influence of the black hole is tiny compared to the host galaxy, a fine tuning of the growth of both is required to produce a tight relation, as is observed.

Is this a casual relation?

The hierarchical assembly in a ΛCDM universe naturally results in a correlation after a sufficiently large number of mergers.

At what stage in their lives do galaxies feed their black holes?

What effect does black hole growth have on the evolutionary trajectory of galaxies?

Gültekin et al. (2009)


Populating galaxies with BH

The AGN “quasar” mode:

In the quasar mode, super-massive black holes grow through merging events where black holes coalesce and cold disk gas is driven onto the central black hole. This is the primary mode of black hole growth (Kauffmann & Haeanelt 2000).

The AGN “radio” mode:

In the radio mode, the quiescent hot gas accretes into the central black hole. This ongoing accretion comes from the surrounding hot gas. Such accretion leads to an outflow from the AGN. By energy conservation this outflow can suppress the inflow of cooling gas.

Croton et al 2006


Black hole growth

Croton et al 2006


Croton et al 2006


Quasar mode in galaxy evolution

Fred Hamann http://www.astro.ufl.edu/events/frontiers/presentations11/hamann_frontiers11.pdf


http://www.astro.ufl.edu/events/frontiers/presentations11/hamann_frontiers11.pdf

http://www.astro.ufl.edu/events/frontiers/presentations11/hamann_frontiers11.pdf

AGN activities and IGM heating

Mir Aghaee, Khosroshahi, 2013


Galaxy downsizing: semi-analytic models

Croton et al. 2006: Effect of “radio-mode” feedback on galaxy formation

Feedback produces an exponential cutoff in luminosity distribution at bright end

Croton et al 2006





No feedback

Croton et al 2006





Feedback

No feedback

Croton et al 2006





Feedback

No feedback

Accretion rate “orders of magnitude” below Eddington=> Low-powered radio galaxies providing the feedback

Croton et al 2006


Black hole in the Galaxy


Measuring central black hole massVirial mass measurements based on motions of stars and

gas in nucleus.

Stars:

Advantage: gravitational forces only

Disadvantage: requires high spatial resolutionlarger distance from nucleus

Gas:

Advantage: can be observed very close to nucleus, high spatial resolution not necessarily required

Disadvantage: possible role of non-gravitational forces (radiation pressure)

http://ned.ipac.caltech.edu/level5/March11/Peterson/peterson3.pdf




Black hole detection, M15


VLBI; Observing the event horizon?The Zurich Physics Colloquium

Observing Black Holes with Schwarzschild Radius ResolutionShep Doeleman


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