A quasar is an extremely luminous active galactic nucleus (AGN). It is sometimes known as a quasi-stellar object, abbreviated QSO. The emission from an AGN is powered by a supermassive black hole with a mass ranging from millions to tens of billions of solar masses, surrounded by a gaseous accretion disc. Gas in the disc falling towards the black hole heats up and releases energy in the form of electromagnetic radiation. The radiant energy of quasars is enormous; the most powerful quasars have luminosities thousands of times greater than that of a galaxy such as the Milky Way. Quasars are usually categorized as a subclass of the more general category of AGN. The redshifts of quasars are of cosmological origin.
A supermassive black hole is the largest type of black hole, with its mass being on the order of hundreds of thousands, or millions to billions, of times the mass of the Sun (M☉). Black holes are a class of astronomical objects that have undergone gravitational collapse, leaving behind spheroidal regions of space from which nothing can escape, not even light. Observational evidence indicates that almost every large galaxy has a supermassive black hole at its center. For example, the Milky Way galaxy has a supermassive black hole at its center, corresponding to the radio source Sagittarius A*. Accretion of interstellar gas onto supermassive black holes is the process responsible for powering active galactic nuclei (AGNs) and quasars.
SDSS J0303-0019 is a distant quasar in the z≥6 regime. It is one of the first two quasars discovered that appear to be "dust-free", the other being QSO J0005-0006.
QSO J0005-0006 is a distant quasar in the ~z≥6 regime. It is one of the first two quasars discovered that appear to be "dust-free", the other being QSO J0303-0019. It was the first such discovered, in 2006, and confirmed in the 2010 study.
TON 618 is a hyperluminous, broad-absorption-line, radio-loud quasar and Lyman-alpha blob located near the border of the constellations Canes Venatici and Coma Berenices, with the projected comoving distance of approximately 18.2 billion light-years from Earth. It possesses one of the most massive black holes ever found, at 40.7 billion M☉.
ULAS J1342+0928 is the second-most distant known quasar detected and contains the second-most distant and oldest known supermassive black hole, at a reported redshift of z = 7.54. The ULAS J1342+0928 quasar is located in the Boötes constellation. The related supermassive black hole is reported to be "800 million times the mass of the Sun". At its discovery, it was the most distant known quasar. In 2021 it was eclipsed by QSO J0313-1806 as the most distant quasar.
SMSS J215728.21-360215.1, commonly known as J2157-3602, is one of the fastest growing black holes and one of the most powerful quasars known to exist as of 2021. The quasar is located at redshift 4.75, corresponding to a comoving distance of 2.5×1010 ly from Earth and to a light-travel distance of 1.25×1010 ly. It was discovered with the SkyMapper telescope at Australian National University's Siding Spring Observatory, announced in May 2018. It has an intrinsic bolometric luminosity of 6.95×1014 L☉ (2.66×1041 W) and an absolute magnitude of -32.36.
Pōniuāʻena, also named J100758.264+211529.207 or J1007+2115, is the third most-distant quasar known, with a measured redshift of z = 7.515 or a lookback time of 13.02 billion years. Its 1.5 billion–solar mass black hole is the most distant known black hole with a mass of over one billion solar masses, and models indicate that it must have formed not later than 100 million years after the Big Bang, before reionization. Its discovery was announced in June 2020. Only the quasars ULAS J1342+0928 (z = 7.54) and J0313–1806 (z = 7.64) are known to be more distant.
Direct collapse black holes (DCBHs) are high-mass black hole seeds, putatively formed within the redshift range z=15–30, when the Universe was about 100–250 million years old. Unlike seeds formed from the first population of stars (also known as Population III stars), direct collapse black hole seeds are formed by a direct, general relativistic instability. They are very massive, with a typical mass at formation of ~105 M☉. This category of black hole seeds was originally proposed theoretically to alleviate the challenge in building supermassive black holes already at redshift z~7, as numerous observations to date have confirmed.
Fabio Pacucci is an Italian theoretical astrophysicist and science educator, currently at Harvard University and at the Smithsonian Astrophysical Observatory. He is widely known for his contributions to the study of black holes, in particular the first population of black holes formed in the Universe and high redshift quasars. He discovered the only two candidate direct collapse black holes known so far, and he was in the team that discovered the farthest lensed quasar known. Pacucci is also a science educator, engaged in public talks on astronomy and science in general. Since 2018 he is a collaborator of TED in developing educational videos about science. The four videos released so far were watched by millions of people worldwide and translated into 25 languages.
QSO J0313−1806 was the most distant, and hence also the oldest known quasar at z = 7.64, at the time of its discovery. In January 2021, it was identified as the most redshifted (highest z) known quasar, with the oldest known supermassive black hole (SMBH) at (1.6±0.4)×109 solar masses. The 2021 announcement paper described it as "the most massive SMBH at z > 7". This quasar beat the prior recordsetting quasar, ULAS J1342+0928. In 2023, UHZ1 was discovered, setting a new record for most distant quasar, eclipsing that of QSO J0313−1806.
PSO J172.3556+18.7734 is an astrophysical jet that was discovered in May 2011. It was originally thought to be a quasar by astronomers, but as of March 8, 2021, it is now classified as a cosmic jet. As of 2021, it is the farthest radio-loud quasar discovered with a redshift of 6.82.
SMSS J114447.77–430859.3 or J1144 or J1144–4308 is a very bright (unbeamed) quasar and a supermassive black hole, that appears from Earth to be in the constellation Centaurus at RA 11h44m and Declination –43, near the Southern Cross (Crux). The SkyMapper Southern Survey (SMSS) was used to ascertain its spectral properties.
GLASS-z12 is a Lyman-break galaxy discovered by the Grism Lens-Amplified Survey from Space (GLASS) observing program using the James Webb Space Telescope's NIRCam in July 2022. Spectroscopic observations of GLASS-z12 by the Atacama Large Millimeter Array (ALMA) in August 2022 confirmed that the galaxy has a spectroscopic redshift of 12.117±0.012, making it one of the earliest and most distant galaxies ever discovered, dating back to just 350 million years after the Big Bang, 13.6 billion years ago. ALMA observations detected an emission line associated with doubly ionized oxygen at 258.7 GHz with a significance of 5σ, suggesting that there is very low dust content in GLASS-z12, if not the early universe as well. Also based on oxygen-related measurements, the age of the galaxy is confirmed.
QSO J0439+1634, often referred to by just its coordinates, J0439+1634 or J043947.08+163415.7, is a superluminous quasar, and was for some time considered the brightest quasar in the early universe with a redshift of z = 6.51. It is approximately 12.873 billion light-years away. The brightness of the quasar is equivalent to about 600 trillion luminosities of the Suns with gravitational lensing, without this effect 11 trillion. The quasar-related supermassive black hole has a mass of 700 million solar masses.
UHZ1 is a background galaxy containing a quasar. At a redshift of approximately 10.1, UHZ1 is at a distance of 13.2 billion light-years, seen when our universe was about 3 percent of its current age. This redshift made it the most distant, and therefore earliest known quasar in the observable universe as of 2023. To detect this object, astronomers working at the Chandra X-ray Observatory used the Abell 2744's cluster mass as a gravitational lens in order to magnify distant objects directly behind it. At the time of discovery, it exceeded the distance record of QSO J0313−1806.
