Black Holes and Compact Objects

Black Holes and Compact Objects

When astronomers refer to “compact objects,” they are generally referring to objects significantly more dense than a typical star or a planet. For example, white dwarfs and neutron stars are extremely dense objects that result when their progenitor stars—Sun-like stars or smaller in the case of white dwarfs, and giants in the case of neutron stars—have run out of fuel for fusion. The stars are no longer able to produce a sufficient amount of radiation pressure in their cores to prevent their outer layers from collapsing. When the biggest stars collapse, they can trigger the formation of black holes—regions of space in which gravity is so strong that even light cannot escape. Black holes with masses comparable to that of the Sun are scattered through the Milky Way and neighboring galaxies. Scientists also have found strong evidence of massive black holes—a million or more times more massive than the Sun—in the centers of many galaxies. In fact, one of these supermassive black holes sits at the heart of our very own Milky Way.

Compact objects are subjects of intense research at KIPAC, whose scientists study them using data from the Fermi Gamma-ray Space Telescope. The gamma-ray emissions from pulsars allow researchers to study how their intense, pulsed radiation is produced. Researchers now believe that the type of neutron star called pulsars behave like powerful magnets in which the poles are not aligned with the axis of the star's rotation. The energetic particles emanating from a pulsar form a beacon—similar to the beam of the lighthouse—which periodically sweeps across our line of sight once or twice per revolution. By taking an accurate count of pulsars, KIPAC scientists have been able to estimate how often stellar collapses take place in the Milky Way.

Black Hole Jet

Supermassive black holes, with up to several hundred billion solar masses, are probably hosted at the center of every larger galaxy. Surrounded by accretion disks of magnetized material, the spinning black holes can bundle magnetic field lines along their polar axes, generating extremely energetic jets of charged particles. In this animation from a supermassive black hole simulation, the jet rams into the surrounding accretion disk (infalling hot plasma as white-red near the hole) and causes the disk to align with the black hole spin axis near the black hole.

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