This unprecedented research project is based on near-infrared observations obtained over more than three years with the ISAAC multi-mode instrument at the 8.
Among the stars that are visible in the sky to the unaided eye, roughly one out of three hundred 0. The percentage is much higher among large, cool stars "red giants" - in fact, almost all luminous stars of that type are variable.
Such stars are known as Mira-variables ; the name comes from the most prominent member of this class, Omicron Ceti in the constellation Cetus The Whale , also known as "Stella Mira" The Wonderful Star.
Its brightness changes with a period of days and it is about times brighter at maximum visible magnitude 2 and one of the fifty brightest stars in the sky than at minimum magnitude 10 and only visible in small telescopes [2]. Stars like Omicron Ceti are nearing the end of their life. They are very large and have sizes from a few hundred to about a thousand times that of the Sun.
The brightness variation is due to pulsations during which the star's temperature and size change dramatically. In the following evolutionary phase, Mira-variables will shed their outer layers into surrounding space and become visible as planetary nebulae with a hot and compact star a "white dwarf" at the middle of a nebula of gas and dust.
Several thousand Mira-type stars are currently known in the Milky Way galaxy and a few hundred have been found in other nearby galaxies, including the Magellanic Clouds. Centaurus A NGC is the nearest giant galaxy, at a distance of about 13 million light-years.
It is located outside the Local Group of Galaxies to which our own galaxy, the Milky Way, and its satellite galaxies, the Magellanic Clouds, belong. Centaurus A is seen in the direction of the southern constellation Centaurus. It is of elliptical shape and is currently merging with a companion galaxy, making it one of the most spectacular objects in the sky, cf. ESO Press Photo eso It possesses a very heavy black hole at its centre and is a source of strong radio and X-ray emission.
During the present research programme, two regions in Centaurus A were searched for stars of variable brightness; they are located in the periphery of this peculiar galaxy, cf.
An outer field "Field 1" coincides with a stellar shell with many blue and luminous stars produced by the on-going galaxy merger; it lies at a distance of 57, light-years from the centre.
The inner field "Field 2" is more crowded and is situated at a projected distance of about 30, light-years from the centre.. Under normal circumstances, any team of professional astronomers will have access to the largest telescopes in the world for only a very limited number of consecutive nights each year.
However, extensive searches for variable stars like the present require repeated observations lasting minutes-to-hours over periods of months-to-years.
It is thus not feasible to perform such observations in the classical way in which the astronomers travel to the telescope each time. Centaurus is one of the largest constellations in the night sky — covering over square degrees — and the brightest in the southern hemisphere. For the unaided southern skies observer, the constellation of Centaurus holds a gem within its grasp — Omega Centauri NGC Though visible to the naked eye, it is best observed through a telescope or with binoculars.
This 18, light-year beauty contains literally millions of stars with a density so great at its center the stars are less than 0. It is possible Omega Centauri may be the remains of a galaxy cannibalized by our own. Or an unseen black hole? Now, hop down to Alpha. Known as Rigil Kentaurus, Rigil Kent, or Toliman, is the third brightest star in the entire night sky and the closest star system to our own solar system. Alpha Centauri A and Alpha Centauri B are the individual stars and a distant, fainter companion is called Proxima Centauri — a red dwarf that is the nearest known star to the Sun.
Oddly enough, Proxima Centauri is also a visual double, which is assumed to be associated with Centaurus AB pair.
Resolution of the binary star Alpha Cen AB is too close to be seen by the naked eye, as the angular separation varies between 2 and 22 arc seconds, but during most of the orbital period, both are easily resolved in binoculars or small telescopes. Then stop for a moment to take a look at Beta Centauri. A line made from the other pointer, Alpha Centauri, through Beta Centauri leads to within a few degrees of Gacrux, the star at the top of the cross.
Using Gacrux, a navigator can draw a line with Acrux to effectively determine south. Hadar is also a very nice double star, too. The blue-white giant star primary is also a spectroscopic binary, accompanied by a widely spaced companion separated from the primary by 1. The Centaurus A galaxy was discovered in by Scottish astronomer James Dunlop who described it as a nebula since the existence of distant galaxies was still a subject of debate at that time.
The galaxy was documented in as one of the earliest discoveries of radio emission sources outside of the Milky Way. It was the first and the brightest source of radio emissions in the constellation Centaurus, hence the name.
With the help of the Hubble Space Telescope, the Spitzer Space Telescope and various observatories on Earth, we were able to take photographs of the light coming from the Centaurus A galaxy in a broad spectrum ranging from infrared to ultraviolet light, as well as radio and microwave.
According to the research conducted in visible light, the galaxy seems to have a structure of elliptical galaxies which do not usually have bands of interstellar gas and dust known as a dust lane or dust band. A dust band is the cloud-like smudge that hides the bulge of the Milky Way when we look at it at the night sky. It is a usual feature in spiral galaxies such as our own, but it is also found in Centaurus A.
Simulation models showed a possibility that a more massive elliptical galaxy merged with a smaller spiral galaxy in a collision that took place somewhere between and million years ago. The central bulge of the Centaurus A galaxy is mainly comprised of older red stars. Research conducted in the ultraviolet spectrum showed abundance of blue stars which indicate very high new star formation activity, called starburst.
Blue stars are young hot stars usually found in nebular clouds and remnants of galactic collisions. Images in the infrared spectrum revealed detailed structure of the dusty region probably comprised of multiple rotating disks wrapped around each other.
This might be a remnant of the smaller spiral galaxy assimilated by the large elliptical one. As a result, Philyra gave birth to a hybrid son. Chiron was a well-known and respected teacher of medicine, music and hunting.
He lived in a cave on Mount Pelion and taught many young princes and future heroes. Being the son of the immortal Cronus, Chiron was himself immortal. When the arrow struck him, he was in terrible pain, but stayed alive. Zeus eventually released the centaur from immortality, allowing him to pass, and later placed him among the stars. Centaurus is usually depicted as a centaur sacrificing an animal, represented by the constellation Lupus, to the gods on the altar represented by Ara constellation.
Alpha Centauri is a multiple star system, only 4. It has an apparent magnitude of Alpha Centauri A , the brightest component in the system, has a visual magnitude of The star system Alpha Centauri , however, is brighter than Arcturus.
Alpha Centauri B is another exceptionally bright star in the constellation. It is a main sequence star belonging to the spectral type K1V, slightly smaller than the Sun. It has an apparent magnitude of 1.
The two stars are believed to be roughly the same age, about 4. There is a third star in the Alpha Centauri system. Designated Alpha Centauri C, it is separated by 2. It belongs to the spectral class M5Ve or M5Vie, which means that it is either a small main sequence star or a sub-dwarf.
Its estimated mass is only Proxima Centauri is only 4. However, with an apparent magnitude of The star is classified as an UV Ceti type flare star, which means that it can have sudden changes in brightness.
Its brightness varies between Alpha Centauri is the closest star system to the solar system. If there were observers in the Alpha Centauri system, they would be looking at pretty much the same image of the sky that we see, with the exception of the brightest star in Centaurus missing from their view, and the Sun appearing as a 0.
Beta Centauri is a blue-white giant star, It has an apparent magnitude of 0. It belongs to the spectral class B1III. Beta Centauri is a binary star, with the companion separated from the brighter component by 1. The brighter star, Hadar A, is a spectroscopic binary itself. Hadar A is composed of a pair of identical stars with an orbital period of days. At least one of the stars is a Beta Cephei type variable, a star whose brightness varies as a result of the pulsations of its surface.
Hadar B orbits the primary pair and takes a minimum of to make the trip. The star has an apparent magnitude of 2. The star is also sometimes known as Haratan. Gamma Centauri is a binary star composed of two stars belonging to the spectral type A0, each of apparent magnitude 2. The system is light years from Earth and has a combined apparent magnitude of 2. The two stars orbit each other every 83 years. It is a Beta Cephei type variable star, one exhibiting variations in brightness as a result of the pulsations of its surface.
It has a mean apparent magnitude of 2. Epsilon Centauri is approximately light years distant. Eta Centauri is a very hot class B dwarf, less than 20 million years old. It is a Be star, one that exhibits variable emissions in its hydrogen spectral lines.
It is also classified as a Gamma Cassiopeiae type variable, or a shell star, which is to say that it is a fast rotating star with a disc of gas surrounding it at the equator.
The star rotates with an equatorial speed of kilometres per second and its rotation period lasts less than a day.
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