What are quasar and blazar? And what are the differences between them?

Answer 1

Quasar:
Quasar is a compact halo of matter surrounding the central supermassive black hole of a young galaxy.
Quasars are believed to be powered by accretion of material into supermassive black holes in the nuclei of distant galaxies, making these luminous versions of the general class of objects known as active galaxies.

Blazar: A blazar is a very compact and highly variable energy source associated with a supermassive black hole at the center of a host galaxy. Blazars are among the most violent phenomena in the universe and are an important topic in extragalactic astronomy.

Answer 2

A quasar (contraction of QUASi-stellAR radio source) is an extremely bright and distant astronomical object thought to be the active nucleus of a young galaxy. They were first identified as being high-redshift sources of electromagnetic energy, including radio waves and visible light that were point-like similar to stars rather than extended sources similar to galaxies. While there is some controversy over the nature of these objects, the majority have come to a scientific consensus that a quasar is a compact halo of matter surrounding the central supermassive black hole of a young galaxy.
Although faint when seen optically, their high redshift implies that these objects lie at a great distance from us, making quasars the most luminous objects in the known universe. Quasars are found to vary in luminosity on a variety of time scales. Some vary in brightness every few months, weeks, days, or hours.

A blazar is a very compact and highly variable energy source associated with a supermassive black hole at the center of a host galaxy. Blazars are among the most violent phenomena in the universe and are an important topic in extragalactic astronomy.

Blazars are members of a larger group of Active Galaxies, also termed Active Galactic Nuclei (AGN). However, blazars are not a homogeneous group and can be divided into two: highly variable quasars, sometimes called Optically Violently Variable (OVV) quasars (these are a small subset of all quasars) and BL Lacertae objects ("BL Lac objects" or simply "BL Lacs"). A few rare objects may be "intermediate blazars" that appear to have a mixture of properties from both OVV quasars and BL Lac objects. The name "blazar" was originally coined in 1978 by astronomer Ed Spiegel to denote the combination of these two classes.

Blazars are AGN with a relativistic jet that is pointing in the general direction of the Earth. We observe "down" the jet, or nearly so, and this accounts for the rapid variability and compact features of both types of blazars. Many blazars have apparent superluminal features within the first few parsecs of their jets, probably due to relativistic shock fronts.

Blazars, like all AGN, are ultimately powered by material falling onto a supermassive black hole at the center of the host galaxy. Gas, dust and the occasional star are captured and spiral into this central black hole creating a hot accretion disk which generates enormous amounts of energy in the form of photons, electrons, positrons and other elementary particles. This region is quite small, approximately 10−3 parsecs in size.

There is also a larger opaque torus extending several parsecs from the central black hole, containing a hot gas with embedded regions of higher density. These "clouds" can absorb and then re-emit energy from regions closer to the black hole. On Earth the clouds are detected as emission lines in the blazar spectrum.

Perpendicular to the accretion disk, a pair of relativistic jets carry a highly energetic plasma away from the AGN. The jet is collimated by a combination of intense magnetic fields and power winds from the accretion disk and torus. Inside the jet, high energy photons and particles interact with each other and the strong magnetic field. These relativistic jets can extend as far as many tens of kiloparsecs from the central black hole.

All of these regions can produce a variety of observed energy, mostly in the form of a nonthermal spectrum ranging from very low frequency radio to extremely energetic gamma rays, with a high polarization (typically a few percent) at some frequencies. The nonthermal spectrum consists of synchrotron radiation in the radio to X-ray range, and inverse Compton emission in the X-ray to gamma-ray region. A thermal spectrum peaking in the ultraviolet region and faint optical emission lines are also present in OVV quasars, but faint or non-existent in BL Lac objects.