Rare radio supernova in nearby galaxy is nearest supernova in five years

May 27, 2009 By Robert Sanders
Zooming into the center of the galaxy M82, one of the nearest starburst galaxies at a distance of only 12 Million light years. The left image, taken with the Hubble Space Telescope (HST), shows the body of the galaxy in blue and hydrogen gas breaking out from the central starburst in red. The VLA image (top left) clearly shows the supernova (SN 2008iz), taken in May 2008. The high-resolution VLBI images (lower right) shows an expanding shell at the scale of a few light days and proves the transient source as the result of a supernova explosion in M82. Graphics: Milde Science Communication, HST Image: /NASA, ESA, and The Hubble Heritage Team (STScI/AURA); Radio Images: A. Brunthaler, MPIfR.

(PhysOrg.com) -- The chance discovery last month of a rare radio supernova - an exploding star seen only at radio wavelengths and undetected by optical or X-ray telescopes - underscores the promise of new, more sensitive radio surveys to find supernovas hidden by gas and dust.

"This supernova is the nearest supernova in five years, yet is completely obscured in optical, ultraviolet and due to the dense medium of the galaxy," said Geoffrey Bower, assistant professor of astronomy at the University of California, Berkeley, and coauthor of a paper describing the discovery in the June issue of the journal Astronomy & Astrophysics. "This just popped out; in the future, we want to go from discovery of radio supernovas by accident to specifically looking for them."

Sky surveys like the one just launched by the Allen Telescope Array, which will look for bright but short-lived radio bursts from supernovas, will provide better estimates of the rate of star formation in nearby , Bower said. Radio emissions from supernovas also can help astronomers understand how stars explode and what happens before their cores collapse, since radio emissions are caused when debris from the explosion collides with the stellar wind previously shed by the stars.

Bower's colleagues are Andreas Bunthaler, Karl M. Menten and Christian Henkel of the Max Planck Institute for Radioastronomy in Bonn, Germany; Mark J. Reid of Harvard University's Center for Astrophysics; and Heino Falcke of the University of Nijmegen in the Netherlands.

The radio supernova was discovered on April 8 in M82, a small irregular galaxy located nearly 12 million light years from Earth in the M81 galaxy group, by the Very Large Array, a New Mexico facility operated by the National Radio Astronomy Observatory (NRAO). It was subsequently confirmed by NRAO's Very Long Baseline Array (VLBA), a 10-telescope array whose baseline stretches from Hawaii to the Virgin Islands, providing the sharpest vision of any telescope on Earth.

The Allen Telescope Array, comprising 42 of a planned 350 radio dishes and supported by UC Berkeley and the SETI Institute of Mountain View, Calif., last week began a major survey of the radio sky that should turn up many more such radio supernovas, Bower said. While the VLA and VLBA have very narrow fields of view unsuited to all-sky surveys, the ATA's wide-angle view is ideal for scanning the full sky once a day, which is necessary to find sources that brighten and dim over several days.

"The ATA can detect objects at least 10 times fainter than this radio supernova, which pushes our survey an order of magnitude deeper than other radio surveys with more attention to transient and variable sources. Radio supernovas are a really strong aspect of that survey," he said. "This ( new radio supernova) is the kind of discovery that we would like to make with the Allen Array."

The ATA will compile an updated catalog of radio sources much as the Sloan Digital Sky Survey updated the older Palomar Observatory Sky Survey of visible and infrared objects. At the same time, it will look for radio signals indicative of intelligent life around other stars.

Not all supernovas produce radio emissions, Bower said. If the star has not sloughed off much of its envelope before collapsing inward to form a neutron star or black hole - a classic Type II supernova - then few radio emissions are produced from gas collisions.

On the other hand, supernovas in very active star-forming regions, like the center of M82, should produce copious radio emissions because of the density of gas and dust in the interstellar medium. That same gas and dust blocks optical, ultraviolet and X-rays, however, making radio surveys one of the few options to find and observe such supernovas.

Bower and his colleagues were studying the motion of M82 with the VLBA, which links the VLA and nine other radio telescopes into a very high resolution instrument, when they noticed a very bright radio source - five times brighter than anything else in the galaxy - in the VLA data. The team looked at earlier observations and found the same source, but almost twice as bright, in data taken May 3, 2008. Data from March 24, 2008, showed an even brighter source - 10 times brighter than in April 2009 - while Oct. 29, 2007, data showed no bright radio source.

Extrapolating backward in time, the research team estimates that the star exploded sometime in January 2008, apparently near the very center of the galaxy. The team rejected alternative explanations for the dimming radio source, such as a flare created by a star falling into a supermassive black hole.

The newly discovered supernova is thus the brightest in radio wavelengths in the past 20 years, Bower said, and is one of only a few dozen radio supernovas observed to date.

The team also looked at the complete data from the VLBA and detected a ring structure indicative of a shock wave plunging through the interstellar medium, bolstering its conclusion that it is a supernova. The ring is about 2,000 astronomical units across, consistent with a year-old supernova. (An astronomical unit 93 million miles, the average distance between Earth and the sun.)

Source: University of California - Berkeley (news : web)

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Bapi
not rated yet Aug 16, 2009
Fate of a Star supernovas and mechanism of explosion of supernovas
Authors_;
*Mr. Rupak Bhattacharya-Bsc(cal) Msc(JU) 7/51 purbapalli,po-sodepur dist 24 parganas(north) Kol-110,West Bengal, India
**Professor Pranab kumar Bhattacharya MD(cal) FIC Path(ind) Professor of pathology, institute of post graduate medical education & research,244 a AJC Bose Road, Kolkata-20, west Bengal, India
***Mr.Ritwik Bhattacharya B.com(cal) 7/51 purbapalli, Po-sodepur Dist 24 parganas(north) , Kolkata-110,WestBengal, India
****Miss Upasana Bhattacharya- Student, Mahamyatala, Garia, kol-86
**** Mrs. Dalia Mukherjee BA(hons) Cal Swamiji Road, south Habra, 24 Parganas(north) West Bengal, India
Dr Avisnata Das MBBS(cal) Ex House physician, Medical college, Kolkata, West Bengal, India
****Dr. Srabani Chakraborty MD(cal); Asst. Professor Pathology, IPGME&R, Kolkata-20

Stars last too long in the universe. For an astronomers to see any evolution of a star or death of a star, in the course of his/their life time, unless he/they is/are lucky enough to see one star destroying itself in a supernova or in a nova explosion or turning towards a Red giant . My old and recently diseased father , late Mr. Bholanath Bhattacharjee of 7/51 purbapali, po-sodepur,24 parganas(north) kol-110, West Bengal, India ,used to teach our brothers and sister in our young ages, with his built up notion like this%u201D%u2026.. Stars are long lived objects with ages, they are as old as our galaxy is, as old as our universe is and they are symbol of eternity they may be 2.5 billion years %u2013 3 billion years old from a first generation stars explosions and are almost perfect cosmic mile markers even very close to Big Bang. Today we know that looking at a supernova of a very distant star almost at horizon of the universe, or of a Nebula, we can understand the mystery of creation of the Universe, the Big Bang it self. They are really the symbol of the eternity. Edington suspected, that the nuclear reactions in the interior of the stars are primary sources of energy for it%u2019s luminosity and fusion of hydrogen to make Helium and that can take place in it, in time bound scale for this ranges, from millions to millions years. Our sun has lost it%u2019s brightness by more then 1% from it%u2019s birth, due to change in it%u2019s internal structure for past 107 years. But the question remains how these supernovas explode? What is the mechanism behind it? No physics probably answered it. Here may be some explanations by my brothers Rupak Bhattacharya and Ritwik Bhattacharya the authors.If we consider the mode of generation of energy in the star, nuclear process provide the only source of energy adequate to keep the stars ongoing luminous. The nuclear fusion in which Hydrogen is built up into Helium, can function sufficient fast at temperature, like those at central core of star (12-25 million degrees). The Helium burning process are important 1) Carbon Nitrogen cycle at which a carbon-12 nucleus (12C) capture proton and is converted into 13C, Nitrogen-4 and nitrogen %u201315. At a final temperature, a proton leads to a fusion yielding original 12C nucleus to a Helium nucleus .2) The Proton- Proton process, in which protons are built direct Helium nuclei through steps, involving first in production of a deuterium and helium3 nuclei to form Helium4 nucleus and two protons. 3) Carbon burning process where 12C nucleus undergoes fusion reaction in the interior of a star producing neutron, proton, and Alfa particles with huge temperature. The first reaction probably dominates into the star, applicable to more massive stars then Sun. The second and third reaction is applicable for Sun and in less massive stars then Sun respectively. Thermonuclear reactions like those in a hydrogen bomb are powering the Sun in a contained and continuous explosions converting some four hundred millions tons (4x1014 grams) of hydrogen into helium. When we look up in the sky in night and see the stars we see them shining because of distant nuclear fusion in them .But hydrogen fusion can not continue for ever. Our Sun is ~ 4.7109 years old star. The energy produced in our ordinary star Sun in each second, is equivalent to the destruction of 41/2 millions tons of hydrogen mass in every second, a mere fleabite compared with the mass of the Sun which is two thousand billion and billion tones. In the Sun or in any other stars, there is limited so much hydrogen in it%u2019s hot interior. Although Helium is predominating as net fusing of Hydrogen, other elements like %u201Ccarbon%u201D, %u201CIron%u201D, %u201CL element%u201D %u201CManganese%u201D %u201CChromium%u201D, EU, yttrium, Magnesium, SR, Nickel, Osmium are also built up in the interior of the stars. Arnett and Truran [Arnett W.D and Truran. JW %u2013Astrophysics.J-Vol157;P339,1969] showed that nuclear reaction net work in the sun when 12C nuclei began to under go the fusion reaction in the interior of sun many elements are produced such as12C 12C---- 23Na P 2.238mev----23Mg n 2.623mev------20Ne 27Al 4.616mev and the reaction goes on endlessly. A large number of computed reactions are possible as the liberated neutron and gamma particles begin reaction with all the nuclear species generated within the hydrogen fusion. In fact Arnett and Truran produced 99 different reactions only in 12C carbon burning net work and 23Na,20Ne, 24Mg,27Al,29Si, and some31P elements are also produced. Beside these Li, Be, B ( Known as leptons)are also produced in the stars due to hydrogen burning. Another more most elementary particles are produced in huge quantities. They are Neutrinos or ghost particles due to hydrogen burning procedure ( Professor Pranab Bhattacharya & Mr. Rupak Bhattacharyya). Conversion of hydrogen into helium in the center of the stars or of the Sun, not only accounts for Sun%u2019s brightness in photons of visible light. It also produces a radiance of a more ghostly kind. The sun glows faintly in neutrinos , which like photons, weight nothing and travel at speed of light. Neutrinos emitted from Sun carry an intrinsic angular momentum or spin while photons has no spin. Matter is transparent to neutrinos which can pass effortlessly through the earth and through the Sun. Only a tiny fraction of them is stopped by intervening matter. As you look up our sun, a billions neutrinos pass through your eye ball. They are not stopped by Retina as ordinary photons do ,but continue unmolested through the back of your head. The curious part is that if at night if I look down at ground, towards the place where sun would be, almost exactly same numbers of solar neutrinos pass through my eye ball, pouring through an interposed earth which is as transparent to neutrinos as a plane of clear glass is to visible light. Neutrinos on very rare occasion convert chlorine atoms into argon atoms with the same number of protons and neutrons. Davis first used a beautiful technique of Pontecours and Alvarez based on the reaction 37C1(V,e-)37Ar to place an upper limit on the solar neutrinos flux on earth



The previous view regarding the %u201CL atoms elements%u201D was that each star makes it%u2019s own share of these %u201CL atoms elements%u201Di.e (autogenously origin). But the concept of autogenic view has been now abandoned, because highest abundance values for stellar Li & Be have shown to be not larger than interstellar upper limit. The formation of each %u201CL atoms%u201D requires the acceleration of about 1erg fast proton. To account auto genetically for lithium abundance in T. Tauri stars (L1/H=109), the time integrated amount production of energy into particle acceleration must be comparable with gravitational release, implying an unlikely high efficiency for acceleration mechanism. So nuclear mechanism is responsible for generation of %u201CL atoms%u201D in the star. It involves high-energy process (Thermonuclear reactions). These L atoms%u201D can be formed in two different ways within the stellar interiors. By the collision of incident light particles on the heavier atoms of interstellar gas (For instance fast protons on stationary C, N, O) or the reverse (for instance fast C, N, O on hydrogen at rest). In the first case the Products %u201C L atoms are to remain in rest, while in the second case, the products are moving at a velocity comparable with that of cosmic rays. The fate of %u201C L atoms%u201D generated by fast protons on stationary C, N, O stationary atoms and are all rapidly thermalised and become part of ISM. %u201CL atoms%u201D generated by reverse process have a fate which depends on the initial energy of %u201CL atoms%u201D. L atoms with energy E 0.3Gev neucleon-1 will suffer nuclear transformation of various elements in the stellar interior.Analysis of Old stars can give us some idea that heavy elements are produced in the interior of the stars and are subsequently ejected into the ISM either through the supernova explosion or through stellar winds or through cosmic rays. The total mass loss, from all stars in a galaxy will be roughly 1MO per year. A fraction of these accumulate in the galactic nuclei, which are center of the gravitational attraction. The halo of our galaxy is nearly spherical region containing very old stars, which have a smaller content of heavy elements than our sun has. It is usually assumed that some how cloud of gas condensed to form our galaxy and that the halo stars were formed during the collapse process and left with a nearly spherical distribution. These stars are ultra high velocity stars. These stars show weak spectral lines corresponding to abundance of carbon and heavier elements [relative to hydrogen] that are lower than our Sun. Because these stars are oldest in our galaxy quite distinct type of nuclear process have been postulated for different groups of elements. The most abundant nuclei are 32S and 58Fe those can be formed by silicon burning process while 16O, 20Ne,23Na 24Mg,28S may be produced by explosive carbon burning process. When heavier elements notably Sr, Y, Zr, Ba etc require neutron capture on slow time scale, by iron group nucleotide already present in the star. A peculiar type of star 73 DRA has been investigated for many a time. It is full of chromium with europium and strontium. The star showed the presence of Cr, Eu, Sr and also Mn, Fe, Ni, in gaseous form while osmium (z=76) is present in both neutral and ionized form. The importance of these heavy elements is that, some of them such as Iridium, gold, uranium are also produced in the stars in the gamma process of nucleus synthesis [Neutron capture slow process]So Helium, L atoms, Carbon, Iron, gold, chromium, nickel, silicon and many other elements are built up in the stellar interior. Although the net fusing of hydrogen into helium dominates however at this stage. Helium builds up in the core. The supply of hydrogen fuel diminishes and eventually becomes in sufficient to provide energy to hold up the strain position. As the energy production decreases, the core of the star contracts and heats up through release of gravitational energy. With a hotter center there is a greater outward pressure and the outer layer of the star expands, so that the star now becomes a RED GIANT. The red giant has a radius hundred times that of a sun. Mean while in the hotter core a new series of fusion reactions begins and with the helium as the fuel many elements like carbon oxygen, neon, magnesium. When helium will exhaust as a fuel, the carbon burning process will start as 12C as a fuel in the star. In any star the internal temperature and density and therefore the rate at which the energy is generated depend sensitively on the opacity of the stellar material or in other words, on the ease with which the photons can escape from the stellar core. In simple terms you can say greater the opacity harder it is for heat to get out making core hotter. Opacities in normal star can be calculated reliably from knowledge for the abundance of the constituent elements and their ionization site
Suernova-: Another important thing in our universe are the supernovas or novas. The supernovas are the explosion of the central core or outer core of a giant massive star. These supernovas are found in the biniary star system. A star may end its life cycle either in the form of a RED GIANT or in the form of a white dwarf or in the form of a %u201C black Dwarf%u201D or in the form of %u201C neutron Star%u201D or in Black Hole%u201D or in the form of Supernova Explotion%u201D. When the explosion of a star occurs in small scale, we call it Nova. In Big bang concept, apart from hydrogen, a little helium was produced. Every atom of every element had been built up by the nuclear fusion reaction in the stellar pressure cooker. The elements only could arrive in the interstellar space to mingle in the clouds of forminig protostars is through this supernovas Novas are however quite different from supernovas. Novas occur in biniary star system and are powered by silicon or carbon fusion. Supernovas occur in single associated with old population II stellar system such as elliptic galaxies and in globular clusters. The classical supernovas are therefore a subset of the cataclysmic variable class of objects, which undergoes out bursts with peak luminiocity ~ 5x1037 to 5x 1038 ergs S-1 in every 104 to 105 years. Around 10-5 to 10-4 MO material are ejected at velocity typically 1000 Kms-1 at each outburst of supernova. The central system is a semi detached binary stars, containing a white dwarf . Classical supernova out burst was observed in 1901, where as dwarf nova out burst was first observed in 1986.Supernovas are two types Type-1(SN-I) and Type 2(SN_II) supernovas. Most astronomers agree that a type 1a supernova starts with a white dwarf %u2014 an aging star that crams as much mass as the sun into a volume no bigger than Earth. Most white dwarfs are cold and inert. But if the star has a companion, it will siphon mass off the neighbor star until tipping the scales at about 1.4 solar masses. At that mass, the white dwarf becomes dense and hot enough to initiate an explosion.mass accreting white dwarfs, in close binary system of stars are Type-1 supernovas, while low mass (M70t in close binary system of stars are Type-1 supernovas, while low mass (M70t in close binary system of stars are Type-1 supernovas, while low mass (M70t

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