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A galaxy is a system of stars, stellar remnants, interstellar gas, dust, and dark matter bound together by gravity. The word is derived from the Greek galaxias (γαλαξίας), literally 'milky', a reference to the Milky Way galaxy that contains the Solar System. Galaxies, averaging an estimated 100 million stars, range in size from dwarfs with less than a thousand stars, to the largest galaxies known – supergiants with one hundred trillion stars, each orbiting its galaxy's center of mass. Most of the mass in a typical galaxy is in the form of dark matter, with only a few percent of that mass visible in the form of stars and nebulae. Supermassive black holes are a common feature at the centres of galaxies.
The following is a timeline of galaxies, clusters of galaxies, and large-scale structure of the universe.
The Andromeda Galaxy is a barred spiral galaxy and is the nearest major galaxy to the Milky Way. It was originally named the Andromeda Nebula and is cataloged as Messier 31, M31, and NGC 224. Andromeda has a D25 isophotal diameter of about 46.56 kiloparsecs (152,000 light-years) and is approximately 765 kpc (2.5 million light-years) from Earth. The galaxy's name stems from the area of Earth's sky in which it appears, the constellation of Andromeda, which itself is named after the princess who was the wife of Perseus in Greek mythology.
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, including 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.
The Sextans Dwarf Spheroidal is a dwarf spheroidal galaxy that was discovered in 1990 by Mike Irwin as the 8th satellite of the Milky Way, located in the constellation of Sextans. It is also an elliptical galaxy, and displays a redshift because it is receding from the Sun at 224 km/s. The distance to the galaxy is 320,000 light-years and the diameter is 8,400 light-years along its major axis.
The Milky Way has several smaller galaxies gravitationally bound to it, as part of the Milky Way subgroup, which is part of the local galaxy cluster, the Local Group.
Galaxy mergers can occur when two galaxies collide. They are the most violent type of galaxy interaction. The gravitational interactions between galaxies and the friction between the gas and dust have major effects on the galaxies involved, but the exact effects of such mergers depend on a wide variety of parameters such as collision angles, speeds, and relative size/composition, and are currently an extremely active area of research. Galaxy mergers are important because the merger rate is a fundamental measurement of galaxy evolution and also provides astronomers with clues about how galaxies grew into their current forms over long stretches of time.
UDFy-38135539 is the Hubble Ultra Deep Field (UDF) identifier for a galaxy which was calculated as of October 2010 to have a light travel time of 13.1 billion years with a present proper distance of around 30 billion light-years.
The thick disk is one of the structural components of about 2/3 of all disk galaxies, including the Milky Way. It was discovered first in external edge-on galaxies. Soon after, it was proposed as a distinct galactic structure in the Milky Way, different from the thin disk and the halo in the 1983 article by Gilmore & Reid. It is supposed to dominate the stellar number density between 1 and 5 kiloparsecs above the galactic plane and, in the solar neighborhood, is composed almost exclusively of older stars. Its stellar chemistry and stellar kinematics are also said to set it apart from the thin disk. Compared to the thin disk, thick disk stars typically have significantly lower levels of metals—that is, the abundance of elements other than hydrogen and helium.
ASW0009io9 (9io9) is a gravitationally lensed system of two galaxies. The nearer galaxy is approximately 2 billion light-years (610 Mpc) from Earth and is designated SDSS J020941.27+001558.4, while the lensed galaxy is 10 billion light-years (3.1 Gpc) distant and is designated ASW0009io9. It was discovered in January 2014 by a group of citizen scientists, while classifying images on the website Spacewarps.org. The discovery was announced on the BBC television programme Stargazing Live.
Cosmos Redshift 7 is a high-redshift Lyman-alpha emitter galaxy. At a redshift z = 6.6, the galaxy is observed as it was about 800 million years after the Big Bang, during the epoch of reionisation. With a light travel time of 12.9 billion years, it is one of the oldest, most distant galaxies known. The name was also inspired by the Portuguese footballer Cristiano Ronaldo.
NGC 3631 is a spiral galaxy located in the constellation Ursa Major. It is located at a distance of about 35 million light years from Earth, which, given its apparent dimensions, means that NGC 3631 is about 60,000 light years across. It was discovered by William Herschel on April 14, 1789. It is a grand design spiral galaxy seen face on.
Red nuggets is the nickname given to rare, unusually small galaxies packed with large amounts of red stars that were originally observed by the Hubble Space Telescope in 2005. They are ancient remnants of the first massive galaxies. The environments of red nuggets are usually consistent with the general elliptical galaxy population. Most red nuggets have merged with other galaxies, but some managed to stay unscathed.
The Giant GRB Ring is a ring of 9 gamma-ray bursts (GRBs) that may be associated with one of the largest known cosmic structures. It was discovered in July 2015 by a team of Hungarian and American astronomers led by L.G. Balazs while analyzing data from different gamma-ray and X-ray telescopes, in particular the Swift Spacecraft.
TOI-561 is an old, metal-poor, Sun-like star, known to have multiple small planets. It is an orange dwarf, estimated to be 10.5 billion years old, and about 79% the mass and 85% the radius of Sol, Earth's sun. It is located in the constellation Sextans, near the border with Leo.
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.
François Hammer, born on 19 November 1958, is a French astrophysicist. He has been an astronomer at the Paris Observatory since 1987 and was an astronomer attached to the Canada-France-Hawaii Telescope between 1991 and 1992.
References
- ↑ Rowland, Lucie E.; et al. (24) (9 May 2024). "REBELS-25: Discovery of a dynamically cold disc galaxy at z = 7.31". Monthly Notices of the Royal Astronomical Society. 535 (3): 2068–2091. arXiv: 2405.06025 . Bibcode:2024MNRAS.535.2068R. doi: 10.1093/mnras/stae2217 .
- ↑ "Astronomers Discover Most Distant Rotating Disk Galaxy: REBELS-25 | Sci.News". Sci.News: Breaking Science News. 8 October 2024. Retrieved 11 October 2024.
- ↑ "REBELS-25 is a dynamically cold disk galaxy, observations find". phys.org. Retrieved 11 October 2024.
- ↑ "Astronomers' discovery of distant Milky Way-like galaxy challenges our theories of how cosmos evolved". 16 October 2024.
- ↑ "Record-breaking ancient spinning galaxy challenges cosmic evolution theories". Space.com . 8 October 2024.
- ↑ "Astronomers Discover Most Distant Rotating Disk Galaxy: REBELS-25 | Sci.News". 8 October 2024.
- ↑ Rowland, Lucie E.; Hodge, Jacqueline; Bouwens, Rychard; Piña, Pavel E Mancera; Hygate, Alexander; Algera, Hiddo; Aravena, Manuel; Bowler, Rebecca; Da Cunha, Elisabete; Dayal, Pratika; Ferrara, Andrea; Herard-Demanche, Thomas; Inami, Hanae; Van Leeuwen, Ivana; De Looze, Ilse; Oesch, Pascal; Pallottini, Andrea; Phillips, Siân; Rybak, Matus; Schouws, Sander; Smit, Renske; Sommovigo, Laura; Stefanon, Mauro; Van Der Werf, Paul (2024). "REBELS-25: Discovery of a dynamically cold disc galaxy at z = 7.31". Monthly Notices of the Royal Astronomical Society. 535 (3): 2068–2091. Bibcode:2024MNRAS.535.2068R. doi: 10.1093/mnras/stae2217 .
- ↑ "Astronomers just found a galaxy way too advanced for its time". Mashable . 8 October 2024.
- ↑ "Astronomers Discover Most Distant Rotating Disk Galaxy: REBELS-25 | Sci.News". 8 October 2024.
- ↑ "Discovery of most distant rotating disk galaxy challenges current formation theories".
- ↑ https://scitechdaily.com/astronomers-baffled-by-ancient-galaxy-that-mirrors-modern-milky-way/
- ↑ Le Conte, Zoe A.; Gadotti, Dimitri A.; Ferreira, Leonardo; Conselice, Christopher J.; De Sá-Freitas, Camila; Kim, Taehyun; Neumann, Justus; Fragkoudi, Francesca; Athanassoula, E.; Adams, Nathan J. (11 May 2024). "Monthly Notices of the Royal Astronomical Society". academic.oup.com. 530 (2): 1984–2000. arXiv: 2309.10038 . doi: 10.1093/mnras/stae921 . Retrieved 2024-10-18.
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