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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 non-standard cosmology is any physical cosmological model of the universe that was, or still is, proposed as an alternative to the then-current standard model of cosmology. The term non-standard is applied to any theory that does not conform to the scientific consensus. Because the term depends on the prevailing consensus, the meaning of the term changes over time. For example, hot dark matter would not have been considered non-standard in 1990, but would be in 2010. Conversely, a non-zero cosmological constant resulting in an accelerating universe would have been considered non-standard in 1990, but is part of the standard cosmology in 2010.
The observable universe is a ball-shaped region of the universe comprising all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time; the electromagnetic radiation from these objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. Initially, it was estimated that there may be 2 trillion galaxies in the observable universe. That number was reduced in 2021 to only several hundred billion based on data from New Horizons. Assuming the universe is isotropic, the distance to the edge of the observable universe is roughly the same in every direction. That is, the observable universe is a spherical region centered on the observer. Every location in the universe has its own observable universe, which may or may not overlap with the one centered on Earth.
In the fields of Big Bang theory and cosmology, reionization is the process that caused electrically neutral atoms in the universe to reionize after the lapse of the "dark ages".
In astronomical spectroscopy, the Lyman-alpha forest is a series of absorption lines in the spectra of distant galaxies and quasars arising from the Lyman-alpha electron transition of the neutral hydrogen atom. As the light travels through multiple gas clouds with different redshifts, multiple absorption lines are formed.
In physical cosmology, structure formation is the formation of galaxies, galaxy clusters and larger structures from small early density fluctuations. The universe, as is now known from observations of the cosmic microwave background radiation, began in a hot, dense, nearly uniform state approximately 13.8 billion years ago. However, looking at the night sky today, structures on all scales can be seen, from stars and planets to galaxies. On even larger scales, galaxy clusters and sheet-like structures of galaxies are separated by enormous voids containing few galaxies. Structure formation attempts to model how these structures were formed by gravitational instability of small early ripples in spacetime density or another emergence.
The diffuse extragalactic background light (EBL) is all the accumulated radiation in the universe due to star formation processes, plus a contribution from active galactic nuclei (AGNs). This radiation covers almost all wavelengths of the electromagnetic spectrum, except the microwave, which is dominated by the primordial cosmic microwave background. The EBL is part of the diffuse extragalactic background radiation (DEBRA), which by definition covers the entire electromagnetic spectrum. After the cosmic microwave background, the EBL produces the second-most energetic diffuse background, thus being essential for understanding the full energy balance of the universe.
The Cosmic Origins Spectrograph (COS) is a science instrument that was installed on the Hubble Space Telescope during Servicing Mission 4 (STS-125) in May 2009. It is designed for ultraviolet (90–320 nm) spectroscopy of faint point sources with a resolving power of ≈1,550–24,000. Science goals include the study of the origins of large scale structure in the universe, the formation and evolution of galaxies, and the origin of stellar and planetary systems and the cold interstellar medium. COS was developed and built by the Center for Astrophysics and Space Astronomy (CASA-ARL) at the University of Colorado at Boulder and the Ball Aerospace and Technologies Corporation in Boulder, Colorado.
Lyman continuum photons, shortened to Ly continuum photons or Lyc photons, are the photons emitted from stars or active galactic nuclei at photon energies above the Lyman limit. Hydrogen is ionized by absorbing LyC. Working from Victor Schumann's discovery of ultraviolet light, from 1906 to 1914, Theodore Lyman observed that atomic hydrogen absorbs light only at specific frequencies and the Lyman series is thus named after him. All the wavelengths in the Lyman series are in the ultraviolet band. This quantized absorption behavior occurs only up to an energy limit, known as the ionization energy. In the case of neutral atomic hydrogen, the minimum ionization energy is equal to the Lyman limit, where the photon has enough energy to completely ionize the atom, resulting in a free proton and a free electron. Above this energy, all wavelengths of light may be absorbed. This forms a continuum in the energy spectrum; the spectrum is continuous rather than composed of many discrete lines, which are seen at lower energies.
A Lyman-alpha emitter (LAE) is a type of distant galaxy that emits Lyman-alpha radiation from neutral hydrogen.
The chronology of the universe describes the history and future of the universe according to Big Bang cosmology.
ULAS J1120+0641 was the most distant known quasar when discovered in 2011, surpassed in 2017 by ULAS J1342+0928. ULAS J1120+0641 was the first quasar discovered beyond a redshift of z = 7. Its discovery was reported in June 2011.
Dark Ages Radio Explorer (DARE) is a NASA mission concept, intended to identify redshifted line emission from the earliest neutral hydrogen atoms forming after Cosmic Dawn. The emissions from neutral hydrogen atoms provide unique opportunities to probe the formation of the first stars in the Universe and the period immediately following the Dark Ages of the universe. The planned orbiter would explore the universe as it was from around 80 million years to 420 million years after the Big Bang. The dataset gathered by the mission would provide insight about the formation of the first stars, how the first black holes grew so rapidly, and the reionization of the universe. Computer models of galaxy formation would also be tested. This mission could also add to research on dark matter decay and provide insight for developing lunar surface telescopes that help refind exoplanet exploration of nearby stars.
Green bean galaxies (GBGs) are very rare astronomical objects that are thought to be quasar ionization echos. They were discovered by Mischa Schirmer and colleagues R. Diaz, K. Holhjem, N.A. Levenson, and C. Winge. The authors report the discovery of a sample of Seyfert-2 galaxies with ultra-luminous galaxy-wide narrow-line regions (NLRs) at redshifts z=0.2-0.6.
Tololo 1247-232 is a small galaxy at a distance of 652 million light-years. It is situated in the southern equatorial constellation of Hydra. Visually, Tol 1247 appears to be an irregular or possibly a barred spiral galaxy. Tol 1247 is named after the surveys that were carried at the Cerro Tololo Inter-American Observatory (CTIO), the first of which was in 1976. It is one of nine galaxies in the local universe known to emit Lyman continuum photons.
Haro 11 (H11) is a small galaxy at a distance of 300,000,000 light-years (redshift z=0.020598). It is situated in the southern constellation of Sculptor. Visually, it appears to be an irregular galaxy, as the ESO image to the right shows. H11 is named after Guillermo Haro, a Mexican astronomer who first included it in a study published in 1956 about blue galaxies. H11 is a starburst galaxy that has 'super star clusters' within it and is one of nine galaxies in the local universe known to emit Lyman continuum photons (LyC).
In cosmology, the missing baryon problem is an observed discrepancy between the amount of baryonic matter detected from shortly after the Big Bang and from more recent epochs. Observations of the cosmic microwave background and Big Bang nucleosynthesis studies have set constraints on the abundance of baryons in the early universe, finding that baryonic matter accounts for approximately 4.8% of the energy contents of the Universe. At the same time, a census of baryons in the recent observable universe has found that observed baryonic matter accounts for less than half of that amount. This discrepancy is commonly known as the missing baryon problem. The missing baryon problem is different from the dark matter problem, which is non-baryonic in nature.
Juna Kollmeier is an astrophysicist from the US. She is currently employed at the Carnegie Institution for Science and is the director of the fifth phase of the Sloan Digital Sky Survey, which made its first observations in October, 2020. She has been named director of the Canadian Institute for Theoretical Astrophysics, located at the University of Toronto, and will take up this position in July, 2021.
The Doppler parameter, or Doppler broadening parameter, usually denoted as , is a parameter commonly used in astrophysics to characterize the width of observed spectral lines of astronomical objects. It is defined as
The Teacup galaxy, also known as the Teacup AGN or SDSS J1430+1339 is a low redshift type 2 quasar, showing an extended loop of ionized gas resembling a handle of a teacup, which was discovered by volunteers of the Galaxy Zoo project and labeled as a Voorwerpje.
References
- 1 2 "Cosmic accounting reveals missing light crisis". Carnegie Institution for Science, News. July 8, 2014.
- ↑ Temming, Maria (July 16, 2014). "The Mystery of the Missing Light". Sky & Telescope .
- ↑ Danforth et al., "on arXiv", Submitted to ApJ,
- 1 2 Kollmeier, Juna; Weinberg, David H.; Oppenheimer, Benjamin D.; Haardt, Francesco; et al. (2014). "The Photon Underproduction Crisis". The Astrophysical Journal Letters . 798 (2): L32. arXiv: 1404.2933 . Bibcode:2014ApJ...789L..32K. doi:10.1088/2041-8205/789/2/L32. S2CID 73665428.
- ↑ Shull, Moloney, Danforth, Tilton 2015 , Astrophysical Journal,
- ↑ Khaire & Srianand 2015, [ dead link ], MNRAS Letters,
- ↑ Gurvich, Alex; Burkhart, Blakesley; Bird, Simeon; Haardt, Francesco; Katz, Neal; Davé, Romeel A.; Fardal, Mark; Madau, Piero; Danforth, Charles; Ford, Amanda B.; Peeples, Molly S.; McEwen, Joseph (2017). "The Effect of AGN Heating on the Low-redshift LyαForest". The Astrophysical Journal. 835 (2): 175. arXiv: 1608.03293 . Bibcode:2017ApJ...835..175G. doi: 10.3847/1538-4357/835/2/175 . S2CID 118492908.