Phoenix is a minor constellation in the southern sky. Named after the mythical phoenix, it was first depicted on a celestial atlas by Johann Bayer in his 1603 Uranometria. The French explorer and astronomer Nicolas Louis de Lacaille charted the brighter stars and gave their Bayer designations in 1756.
Phoenix is bordered by Fornax and Sculptor to the north, Grus to the west, Tucana to the south, touching on the corner of Hydrus to the south, and Eridanus to the east and southeast. The constellations Phoenix, Grus, Pavo and Tucana, are known as the Southern Birds. The bright star Achernar is nearby.
The constellation stretches from roughly −39° to −57° declination, and from 23.5h to 2.5h of right ascension. This means it remains below the horizon to anyone living north of the 40th parallel in the Northern Hemisphere, and remains low in the sky for anyone living north of the equator. It is most visible from locations such as Australia and South Africa during late Southern Hemisphere spring. Most of the constellation lies within, and can be located by, forming a triangle of the bright stars Achernar, Fomalhaut and Beta Ceti- Ankaa lies roughly in the center of this.
The ‘southern birds,’ as depicted in Johann Bayer’s Uranometria. Phoenix is on the lower left.
In Greek mythology, a phoenix is a long-lived bird that is cyclically regenerated or reborn. Associated with the sun, it obtains new life by arising from the ashes of its predecessor. According to some sources, the phoenix dies in a show of flames and combustion, although there are other sources that claim that the legendary bird dies and simply decomposes before being born again.
[https://en.wikipedia.org/wiki/Phoenix_(mythology)]
Phoenix was the largest of the twelve constellations established by Petrus Plancius from the observations of Pieter Dirkszoon Keyser and Frederick de Houtman. It first appeared on a 35-cm diameter celestial globe published in 1597 (or 1598) in Amsterdam by Plancius with Jodocus Hondius. The first depiction of this constellation in a celestial atlas was in Johann Bayer’s Uranometria of 1603. De Houtman included it in his southern star catalog the same year under the Dutch name Den voghel Fenicx, ‘The Bird Phoenix,’ symbolizing the phoenix of classical mythology. One name of the brightest star Alpha Phoenicis- Ankaa- is derived from the Arabic ‘al-anqa’ ‘the phoenix,’ and was coined sometime after 1800 in relation to the constellation.
Celestial historian Richard Allen noted that unlike the other constellations introduced by Plancius and La Caille, Phoenix has actual precedent in ancient astronomy, as the Arabs saw this formation as representing young ostriches, Al Ri’al, or as a griffin or eagle. In addition, the same group of stars was sometimes imagined by the Arabs as a boat, Al Zaurak, on the nearby river Eridanus.
The Chinese incorporated Phoenix’s brightest star, Ankaa (Alpha Phoenicis), and stars from the adjacent constellation Sculptor to depict Bakui, a net for catching birds. Phoenix and the neighboring constellation of Grus together were seen by Julius Schiller as portraying Aaron the High Priest. These two constellations, along with nearby Pavo and Tucana, are called the Southern Birds.
[http://astropixels.com/constellations/charts/Phe.html]
[https://60sinseattle.wordpress.com/2012/02/29/phoenix-constellation/]
Ankaa (Alpha Phoenicis) is the brightest star in the constellation. It is an orange giant of apparent visual magnitude 2.37 and spectral type K0.5IIIb, 77 light years distant from Earth and orbited by a secondary object about which little is known.
Located centrally in the asterism, Beta Phoenicis is the second brightest star in the constellation and another binary star. Together the stars, both yellow giants of spectral type G8, shine with an apparent magnitude of 3.31, though the components are of individual apparent magnitudes of 4.0 and 4.1 and orbit each other every 168 years.
Gamma Phoenicis is a red giant of spectral type M0IIIa and varies between magnitudes 3.39 and 3.49. It lies 235 light years away.
Epsilon Phoenicis is an orange giant of spectral type K0III, a star that has used up its core hydrogen and has expanded. Its apparent magnitude is 3.87, and it is located around 144 parsecs (470 ly) distant.
[https://en.wikipedia.org/wiki/Epsilon_Phoenicis]
Delta Phoenicis is a yellow giant star. Its apparent magnitude is 3.95 and is about 142 light years away from earth.
[https://en.wikipedia.org/wiki/Delta_Phoenicis]
Ten stars have been found to have planets to date, and four planetary systems have been discovered with the SuperWASP project.
WISE J003231.09-494651.4 and WISE J001505.87-461517.6 are two brown dwarfs discovered by the Wide-field Infrared Survey Explorer, and are 63 and 49 light years away respectively. Initially hypothesized before they were belatedly discovered, brown dwarfs are objects more massive than planets, but which are of insufficient mass for hydrogen fusion characteristic of stars to occur. Many are being found by sky surveys.
Phoenix contains HE0107-5240, possibly one of the oldest stars yet discovered. It has around 1/200,000 the metallicity that the Sun has and hence must have formed very early in the history of the universe. With a visual magnitude of 15.17, it is around 10,000 times dimmer than the faintest stars visible to the naked eye and is 36,000 light years distant.
The constellation does not lie on the galactic plane of the Milky Way, and there are no prominent star clusters.
Robert’s Quartet (composed of the irregular galaxy NGC 87, and three spiral galaxies NGC 88, NGC 89 and NGC 92) is a group of four galaxies located around 160 million light-years away which are in the process of colliding and merging. They are within a circle of radius of 1.6 arcmin, corresponding to about 75,000 light-years. Located in the galaxy ESO 243-49 is HLX-1, an intermediate-mass black hole- the first one of its kind identified. It is thought to be a remnant of a dwarf galaxy that was absorbed in a collision with ESO 243-49. Before its discovery, this class of black hole was only hypothesized:
Robert’s Quartet
Robert’s Quartet is a family of four very different galaxies, located at a distance of about 160 million light-years, close to the center of the southern constellation of the Phoenix. Its members are NGC 87, NGC 88, NGC 89 and NGC 92, discovered by John Herschel in the 1830s.
NGC 87 (upper right) is an irregular galaxy similar to the satellites of our Milky Way, the Magellanic Clouds. NGC 88 (center) is a spiral galaxy with an external diffuse envelope, most probably composed of gas. NGC 89 (lower middle) is another spiral galaxy with two large spiral arms. The largest member of the system, NGC 92 (left), is a spiral Sa galaxy with an unusual appearance. One of its arms, about 100,000 light-years long, has been distorted by interactions and contains a large quantity of dust.
[https://www.eso.org/public/images/eso0535a/]
Lying within the bounds of the constellation is the gigantic Phoenix cluster, which is around 7.3 million light years wide and 5.7 billion light years away, making it one of the most massive galaxy clusters. It was first discovered in 2010, and the central galaxy is producing an estimated 740 new stars a year:
Phoenix Cluster: A Fresh Perspective on an Extraordinary Cluster of Galaxies
Galaxy clusters are often described by superlatives. After all, they are huge conglomerations of galaxies, hot gas, and dark matter and represent the largest structures in the Universe held together by gravity.
Galaxy clusters tend to be poor at producing new stars in their centers. They generally have one giant galaxy in their middle that forms stars at a rate significantly slower than most galaxies- including our Milky Way. The central galaxy contains a supermassive black holeroughly a thousand times more massive than the one at the center of our galaxy. Without heating by outbursts from this black hole, the copious amounts of hot gas found in the central galaxy should cool, allowing stars to form at a high clip. It is thought that the central black hole acts as a thermostat, preventing rapid cooling of surrounding hot gas and impeding star formation.
New data provide more details on how the galaxy cluster SPT-CLJ2344-4243, nicknamed the Phoenix Cluster for the constellation in which it is found, challenges this trend. The cluster has shattered multiple records in the past: In 2012, scientists announced that the Phoenix cluster featured the highest rate of cooling hot gas and star formation ever seen in the center of a galaxy cluster, and is the most powerful producer of X-rays of all known clusters. The rate at which hot gas is cooling in the center of the cluster is also the largest ever observed.
New observations of this galaxy cluster at X-ray, ultraviolet, and optical wavelengths by NASA’s Chandra X-ray Observatory, the Hubble Space Telescope, and the Clay-Magellan telescope located in Chile, are helping astronomers better understand this remarkable object. Clay-Magellan’s optical data reveal narrow filaments from the center of the cluster where stars are forming. These massive cosmic threads of gas and dust, most of which had never been detected before, extend for 160,000 to 330,000 lights years. This is longer than the entire breadth of the Milky Way galaxy, making them the most extensive filaments ever seen in a galaxy cluster.
These filaments surround large cavities- regions with greatly reduced X-ray emission- in the hot gas. The X-ray cavities can be seen in this composite image that shows the Chandra X-ray data in blue and optical data from the Hubble Space Telescope (red, green, and blue). For the location of these ‘inner cavities,’ mouse over the image. Astronomers think that the X-ray cavities were carved out of the surrounding gas by powerful jets of high-energy particles emanating from near a supermassive black hole in the central galaxy of the cluster. As matter swirls toward a black hole, an enormous amount of gravitational energy is released. Combined radio and X-ray observations of supermassive black holes in other galaxy clusters have shown that a significant fraction of this energy is released as jets of outbursts that can last millions of years. The observed size of the X-ray cavities indicates that the outburst that produced the cavities in SPT- CLJ2344-4243 was one of the most energetic such events ever recorded.
However, the central black hole in the Phoenix cluster is suffering from somewhat of an identity crisis, sharing properties with both ‘quasars,’ very bright objects powered by material falling onto a supermassive black hole, and ‘radio galaxies’ containing jets of energetic particles that glow in radio waves, and are also powered by giant black holes. Half of the energy output from this black hole comes via jets mechanically pushing on the surrounding gas (radio-mode), and the other half from optical, UV and X-radiation originating in an accretion disk (quasar-mode). Astronomers suggest that the black hole may be in the process of flipping between these two states.
X-ray cavities located farther away from the center of the cluster, labeled as ‘outer cavities,’ provide evidence for strong outbursts from the central black hole about a hundred million years ago (neglecting the light travel time to the cluster). This implies that the black hole may have been in a radio mode, with outbursts, about a hundred million years ago, then changed into a quasar mode, and then changed back into a radio mode.
It is thought that rapid cooling may have occurred in between these outbursts, triggering star formation in clumps and filaments throughout the central galaxy at a rate of about 610 solar masses per year. By comparison, only a couple new stars form every year in our Milky Way galaxy. The extreme properties of the Phoenix cluster system are providing new insights into various astrophysical problems, including the formation of stars, the growth of galaxies and black holes, and the co-evolution of black holes and their environment.
[http://chandra.harvard.edu/photo/2015/phoenix/]
Larger still is El Gordo, or officially ACT-CL J0102-4915, a supercluster whose discovery was announced in 2012. Located around 7.2 billion light years away, it is composed of two subclusters in the process of colliding, resulting in the spewing out of hot gas, seen in X-rays and infrared images:
This is a Hubble image of the most massive cluster of galaxies ever seen to exist when the universe was just half its current age of 13.8 billion years. The cluster contains several hundred galaxies.
NASA’s Hubble Space Telescope has weighed the largest known galaxy cluster in the distant universe, catalogued as ACT-CL J0102-4915, and found it definitely lives up to its nickname- El Gordo (Spanish for ‘the fat one’).
By measuring how much the cluster’s gravity warps images of galaxies in the distant background, a team of astronomers has calculated the cluster’s mass to be as much as 3 million billion times the mass of our sun. Hubble data show the galaxy cluster, which is 9.7 billion light-years away from Earth, is roughly 43 percent more massive than earlier estimates.
The team used Hubble to measure how strongly the mass of the cluster warped space. Hubble’s high resolution allowed measurements of so-called ‘weak lensing,’ where the cluster’s immense gravity subtly distorts space like a funhouse mirror and warps images of background galaxies. The greater the warping, the more mass is locked up in the cluster.
A fraction of this mass is locked up in several hundred galaxies that inhabit the cluster and a larger fraction is in hot gas that fills the entire volume of the cluster. The rest is tied up in dark matter, an invisible form of matter that makes up the bulk of the mass of the universe.
Though equally massive galaxy clusters are found in the nearby part of the universe, such as the Bullet cluster, nothing like this has ever been discovered to exist so far back in time, when the universe was roughly half its current estimated age of 13.8 billion years. The team suspects such monster galaxy clusters are rare in the early universe, based on current cosmological models.
The immense size of El Gordo was first reported in January 2012. Astronomers estimated its mass based on observations made by NASA’s Chandra X-ray Observatory, and galaxy velocities measured by the European Southern Observatory’s Very Large Telescope array in Paranal, Chile. They were able to put together estimates of the cluster’s mass based on the motions of the galaxies moving inside the cluster and the temperatures of the hot gas between those galaxies.
The challenge was that El Gordo looked as if it might have been the result of a titanic collision between a pair of galaxy clusters- an event researchers describe as two cosmic cannonballs hitting each other.
The expectation of ‘unaccounted energy’ comes from the fact the merger of galaxy clusters is occurring tangentially to the observers’ line-of-sight. This means they are potentially missing a good fraction of the kinetic energy of the merger because their spectroscopic measurements only track the radial speeds of the galaxies.
[https://www.nasa.gov/press/2014/april/nasa-hubble-team-finds-monster-el-gordo-galaxy-cluster-bigger-than-thought/]
Phoenix is the radiant of two annual meteor showers. The Phoenicids, also known as the December Phoenicids, were first observed on 3 December 1887. The shower was particularly intense in December 1956, and is thought related to the breakup of the short-period comet 289P/Blanpain. It peaks around 4-5 December, though is not seen every year. A very minor meteor shower peaks around July 14 with around one meteor an hour, though meteors can be seen anytime from July 3 to 18; this shower is referred to as the July Phoenicids.
[https://en.wikipedia.org/wiki/Phoenix_(constellation)]
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