Supernova SN 2005AP

SN 2005AP: The Brightest Supernova Yet Found [Credit: SDSS, R. Quimby/McDonald Obs./UT-Austin]

SN 2005AP was an extremely energetic type II supernova. Most Type II supernovae show very broad emission lines which indicate expansion velocities of many thousands of kilometres per second, dominated by broad hydrogen lines that remain for the life of the decline. It is reported to be the brightest supernova yet recorded, twice as bright as the previous record holder, SN 2006GY. It was discovered on 3^rd March 2005 on unfiltered optical images taken with the 0.45 m ROTSE-IIIb (Robotic Optical Transient Search Experiment) telescope, which is located at the McDonald observatory in West Texas, by Robert Quimby as part of the Texas Supernova Search that also discovered SN 2006GY. Although it was discovered before SN 2006GY it was not recognised as being brighter until October 2007. As it occurred 4.7 billion light years from Earth it was not visible to the naked eye.

Although SN 2005AP was twice as bright at its peak as SN 2006GY it was not as energetic overall, as the former brightened and dimmed in a typical period of a few days whereas the latter remained very bright for many months. SN 2005AP was about 300 times brighter than normal for a type II supernova. It has been speculated that this supernova involved the formation of a quark star. Quimby has suggested that the supernova is of a new type distinct from the standard type II supernova and his research group have identified five other supernovae similar to SN 2005AP and SCP 06F6, all of which were extremely bright and lacking in hydrogen.

Technical data for SN 2005AP are: Host galaxy – SDSS J130114+2743; Constellation – Coma Berenices; Right Ascension – 13h 01m 14.84s; Declination – +27° 43′ 31.4″; Distance – 4.7 billion light years

What could cause a bang this big? This supernova explosion was so inherently bright that it could be seen nearly 5 billion light years away (a redshift of 0.28) even with a small telescope. Specific colours emitted during SN 2005AP indicate that it was a Type II supernova, a breed of stellar explosion that results when a high mass star begins fusing heavy elements in or near its core. Type II supernovas may be more powerful than their Type Ia cousins, but they are not currently more useful cosmologically because astronomers don’t understand how to accurately recover their intrinsic brightnesses. It is therefore dimmer Type Ia supernovas that are used by astronomers to calibrate the distance scale of the nearby universe. Were Type II supernova better understood, astronomers might be able to probe distances further into the universe, and so probe the stability of the strange dark energy that dominates the present universe. Pictured above in a digitally compressed image, the bright supernova SN 2005AP is visible on the right where no exploding star had been seen on the left less than three months before.

Supernova SN 2006GY

Unlike typical supernovae that reach peak brightness in days to a few weeks and then dim into obscurity a few months later, SN 2006GY took 70 days to reach full brightness and stayed brighter than any previously observed supernova for more than 3 months. 8 months later, it was still as bright as a typical supernova at its peak, outshining its host galaxy 240 million light years away.

SN 2006GY was an extremely energetic supernova, sometimes referred to as a hypernova or quark-nova, that was discovered on 18^th September 2006. It was first observed by Robert Quimby and P. Mondol, and then studied by several teams of astronomers using facilities that included the Chandra, Lick, and Keck Observatories. In May 2007, NASA and several of the astronomers announced the first detailed analyses of the supernova, describing it as the “brightest stellar explosion ever recorded”. In October 2007 Quimby announced that SN 2005AP had broken SN 2006GY’s record as the brightest ever recorded supernova. Time magazine listed the discovery of SN 2006GY as third in its Top 10 Scientific Discoveries for 2007.

This diagram illustrates the pair production process that astronomers think triggered the explosion in SN 2006GY. A sufficiently massive star can produce gamma rays of such high energy that some of the photons convert into pairs of electrons and positrons causing a runaway reaction which destroys the star.

SN 2006GY and the core of its home galaxy, NGC 1260, viewed in x-ray light from the Chandra X-ray Observatory. The NGC 1260 galactic core is at the lower left and SN 2006GY is at the upper right

SN 2006GY occurred in a distant galaxy (NGC 1260), approximately 238 million light years away. Therefore, due to the time it took light from the supernova to reach Earth, the event occurred about 238 million years ago. Preliminary indications are that it was an unusually high-energy supernova of a very large star, around 150 solar masses, possibly of a type referred to as a pair-instability supernova. The energy released by the explosion has been estimated at 10⁵² ergs (10⁴⁵ J).

A pair instability supernova can only happen in stars that are very massive – having a range of around 130 to 250 solar masses. At a certain point in such a massive star’s life its core begins to produce high energy gamma rays which have a greater energy than the rest mass of two electrons (mass-energy equivalence). These high energy gamma rays strike atomic nuclei and are converted from energy (or heat) to matter, disrupting the equilibrium between thermodynamic pressure and gravity in the star’s core. The sudden drop in thermodynamic pressure causes the core to collapse. As the core collapses it gets hotter and hotter until a runaway thermonuclear reaction begins. In a few seconds, all of the fuel in the core undergoes a cataclysmic thermonuclear fusion, blowing the star completely apart while leaving nothing behind.

Light curve of SN 2006GY (uppermost intermittent squares) compared with other types of supernovae

NASA artist’s impression of the explosion of SN 2006GY

Technical data for SN 2005GY are: Host galaxy – NGC 1260; Constellation – Perseus; Right Ascension – 03h 17m 27.10s; Declination – +41° 24' 19.50"; Distance – 238 million light years; Peak magnitude – +14.2; Progenitor – Hypergiant star located 2.0" W and 0.4" N of the centre of galaxy NGC 1260.

Although the SN 2006GY supernova was intrinsically about one hundred times as luminous as SN 1987A, which was bright enough to be seen by the naked eye, SN 2006GY was more than 1,400 times as far away as SN 1987A, and too far away to be seen without a telescope. Denis Leahy and Rachid Ouyed, Canadian scientists from the University of Calgary have proposed that SN 2006GY was the birth of a quark star. Another possibility is that SN 2006GY is not actually a pair-instability supernova but instead is powered by interaction with a dense circumstellar medium – a Type IIn supernova.

Similarity to Eta Carinæ

Eta Carinæ (η Carinæ or η Car) is a highly luminous hypergiant star located approximately 7,500 light years from Earth in the Milky Way galaxy. Since Eta Carinæ is 32,000 times closer than SN 2006GY, the light from it will be about a billion-fold brighter. It is estimated to be similar in size to the star which became SN 2006GY. Dave Pooley, one of the discoverers of SN 2006GY, says that if Eta Carinæ exploded in a similar fashion, it would be bright enough that one could read by its light here on Earth nights, and would even be visible during the day time. SN 2006GY’s apparent magnitude is 15, so a similar event at Eta Carinæ will have an apparent magnitude of about −7.5. According to astrophysicist Mario Livio, this could happen at any time, but the risk to life on Earth would be low.

Types of Supernovae

Type Ia: A white dwarf star accumulates material from a companion star, raising the temperature of the white dwarf. This results in runaway fusion and the star explodes very violently, releasing energy of the order of 10⁴⁴ Joules. The accompanying shock wave may result in material reaching speed around 3% of that of light. The absolute magnitude is always about −19.3 which allows these stars to be used as “standard candles” to measure the distance of their host galaxies. The spectra of these supernovae show little or no hydrogen.
Other Types (Ib, Ic, II-P, II-L, IIn and IIb): These are all caused by the collapse of the core of a very massive star whose gravity is greater than the pressure of fusion at its core. The collapse may cause violent expulsion of the outer layers of the star resulting in a supernova, or the release of gravitational potential energy may be insufficient and the star may collapse into a black hole or neutron star with little radiated energy. The types indicate differences in the spectrum of the star.

Much more information is on Wikipedia .

Supernova SN 2011FE in the Pinwheel Galaxy (M 101)

A supernova explosion in the Pinwheel Galaxy (M 101 in Ursa Major). The spectacular explosion of a star, SN 2011FE, in a distant galaxy has given astronomers a rare glimpse of how supernovae blast the basic ingredients for life into the cosmos. The position of the supernova is shown by the head of the arrow, the ‘blob’ at the tail having no significance.
[Photograph: Press Association]

Scientists captured images of the colossal detonation in the Pinwheel galaxy 21 million light years away within hours of the burst of light from the explosion reaching Earth.The first observations of the supernova were made by the Liverpool Telescope at La Palma in the Canary islands and followed within hours by the Shane Telescope at Lick Observatory in California and the Keck I Telescope on Mauna Kea. The supernova, called SN 2011FE, was the result of a thermonuclear explosion that tore the parent star apart, converting carbon and oxygen into heavier elements, such as nickel, in the process. NASA’s Swift space telescope turned its sensors towards the exploding star moments after observations began at three powerful ground-based telescopes. “We caught the supernova just 11 hours after it exploded, so soon that we were later able to calculate the actual moment of the explosion to within 20 minutes,” said Peter Nugent at the US department of energy’s Berkeley Lab in California.

Watching the star explode gave scientists a unique insight into how elements created in the supernova spewed out into space in the expanding fireball. The telescopes recorded oxygen, magnesium, silicon, calcium and iron being flung out at 16,000 kilometres a second, around 5% of the speed of light. “Understanding how these giant explosions create and mix materials is important because supernovae are where we get most of the elements that make up the Earth and even our own bodies. For instance, these supernovae are a major source of iron in the universe. So we are all made of bits of exploding stars,” said Mark Sullivan at Oxford University.

The observations gave scientists fresh details of what triggers this class of stellar explosion, known as a ‘type 1a’ supernova. This kind of supernova is important because it always produces the same amount of light. Monitoring their brightness has allowed astronomers to calculate the rate of expansion of the universe. From the results they gathered, the scientists worked out that the explosion began with a white dwarf star made of carbon and oxygen. This kind of star can grow to around 1.4 times the mass of the sun before gravity causes it to collapse in on itself.

“What caused these explosions has divided the astronomical community deeply. SN 2011FE is like the Rosetta Stone of ‘type 1a’ supernovae,” said Shri Kulkarni, a co-author on the study at the California Institute of Technology. The research is published in the journal Nature.

A Massive Gamma Ray Burst, GRB 130472A

An artist’s impression of a huge gamma ray burst

In April 2013, an incredibly bright flash of light, named GRB 130472A, burst from the direction of the constellation Leo. Originating billions of light-years away, this explosion of light, called a gamma-ray burst, has now been confirmed as the brightest ever observed. The blast was observed by several space- and ground-based telescopes, and the data were analyzed by dozens of astronomers around the world. The Fermi Gamma-ray Space Telescope was the first to detect the event, and it quickly began monitoring the flood of radiation using its Large Area Telescope (LAT).

Several features of GRB 130472A combined to make it of particular interest to astronomers.

First, the blast occurred 3.6 billion light-years away from Earth, which is less than half the distance of the typical GRB. The record-setting 20 hours that the LAT observed gamma rays was longer than any other observed GRB. And, in addition to being the brightest GRB ever witnessed, it was also one of the most energetic. The leading theory explaining long gamma-ray bursts such as GRB 130427A suggests that they are created during the most energetic explosions in the cosmos, which occur when a very massive star collapses on itself. These explosions expel a jet of elementary particles travelling at close to the speed of light. Within the jet, pressure, temperature and density are not uniform, creating internal shock waves that move inward and outward as faster regions within the jet collide with slower ones. As the jet travels outward, it collides with the interstellar medium to create additional shock waves, called external shocks. Although details are not well understood, particles are accelerated at the shock front and, at the same time, interact with the surrounding electromagnetic fields. This causes particles to lose part of their energy emitting photons, through a process known as synchrotron radiation. The balance between the gain in energy from acceleration by the shock and the loss of energy due to synchrotron radiation dictates the maximum energy of the photons that can be emitted by such a system. The highest energy photons among these are classified as gamma rays and are detected by the LAT.

The observations of GRB 130472A, however, didn’t quite match energy levels predicted by current models. For instance, the telescopes detected more photons, and more high-energy gamma rays, than theoretical models would predict for a burst of this magnitude. In particular, a few of these high-energy events are so energetic that they cannot be produced via existing models of synchrotron radiation from shock-accelerated particles. Additionally, the prevailing thought was that the brightest flashes were driven by the explosion’s internal shock waves, but the evidence indicates that these photons were created externally.

The new observations don’t rule out the existing model, but researchers will need to either amend portions of it or adopt a new theory altogether to account for these characteristics. The microphysics of how particles are accelerated involves a certain amount of well-thought assumptions, and these assumptions therefore get built into the theoretical models used to predict the behaviour of cosmic events. The assumptions are necessary in part because these events cannot be recreated in laboratory settings, which highlights the critical role that observations play in the fine-tuning of fundamental physics theories. Giacomo Vianello, a postdoctoral scholar and a co-author who performed LAT data analysis, said:

The really cool thing about this GRB is that because the exploding matter was travelling at [nearly] the speed of light, we were able to observe relativistic shocks. We cannot make a relativistic shock in the lab, so we really don’t know what happens in it, and this is one of the main unknown assumptions in the model. These observations challenge the models and can lead us to a better understanding of physics.

The findings are reported in a series of papers published by the journal Science at the Science Express website on 21^st November 2013. And see also the Guardian’s report.

Mystery Object SCP 06F6

SCP 06F6 is (or was) an astronomical object of unknown type, discovered on 21^nd February 2006 in the constellation Boötes during a survey of galaxy cluster CL 1432.5+3332.8 with the Hubble Space Telescope’s Advanced Camera for Surveys Wide Field Channel.

The sudden appearance of the transient “mystery object” SCP 06F6 in Hubble’s field of view. The lower image quadrant represents a zoomed in view. New research by astrophysicists at the University of Warwick has discovered that a mystery stellar explosion recorded in 2006 may have marked the unusual death of an equally unusually carbon-rich star. [Credit: NASA, ESA, and K. Barbary (University of California, Berkeley)]

According to research by the Supernova Cosmology Project, the object brightened over a period of roughly 100 days, reaching a peak intensity of magnitude 21; it then faded over a similar period. They report that the spectrum of light emitted from the object does not match known supernova types, and is dissimilar to any known phenomena in the Sloan Digital Sky Survey database. The light in the blue region shows broad line features, while the red region shows continuous emission. The spectrum shows a handful of spectral lines, but when astronomers try to trace any one of them to an element the other lines fail to match up with any other known elements.

Because of its uncommon spectrum, the team was not able to determine the distance to the object using standard redshift techniques; it is not even known whether the object is within or outside the Milky Way. Furthermore, no Milky Way star or external galaxy has been detected at this location, meaning any source is very faint. The European X-ray satellite XMM Newton made an observation in early August 2006 which appears to show an X-ray glow around SCP 06F6, two orders of magnitude more luminous than that of supernovae. Observations from the Palomar Transient Factory reported in 2009, indicate a redshift z = 1.189 and a peak magnitude of −23.5 absolute (comparable to SN 2005AP) making SCP 06F6 one of the most luminous transient phenomenon known as of that date.

Supernovae reach their maximum brightness in only 20 days, and then take much longer to fade away. Researchers had initially conjectured that SCP 06F6 might be an extremely remote supernova; relativistic time dilation might have caused a 20-day event to stretch out over a period of 100 days. But this explanation now seems unlikely. Other conjectures that have been advanced involve a collision between a white dwarf and an asteroid, or the collision of a white dwarf with a black hole.

An analysis by a team from the University of Warwick suggests that the light spectrum is “consistent with emission from a cool, carbon-rich atmosphere at a redshift of z ∼ 0.14”, possibly representing the core collapse and explosion of a carbon star. Groups agree that SCP 06F6 may represent “a new class” of celestial object.

The analysis of Israeli astronomers of Technion, suggest four alternative explanations for SCP 06F6, in plausibility order: the tidal destruction of a CO white dwarf by an intermediate-mass black hole, a type Ia supernova exploding inside the dense stellar wind of a carbon star, an asteroid that was swallowed up by a white dwarf or, least likely, a core-collapse supernova. Observations in 2009 indicate that it may be a pair-instability supernova. The event was similar to SN 2005AP, and other unusually bright supernova suggesting that it was a new type of supernova.

However, to achieve the close match, SCP 06F6 must be at a distance of around 2 billion light years, causing a considerable redshift in its appearance. Given the large distance, the sudden appearance of SCP 06F6 is most likely related to the sudden death of a carbon-rich star, and the Warwick team believes that this object may be a new type of a totally new class of supernova. It would be an unusual type of supernovae in several aspects: SCP 06F6 is located in a blank part of the sky, with no known visible host galaxy. If the star did explode as a normal type II supernova why then did it take up to four times as long to brighten and diminish as other such supernova and why did emit up to 100 times more X-rays energy than expected? The X-ray energy might lead one to speculate that the star was ripped apart by a black hole rather than exploding on its own, but the lead researcher of University of Warwick team says that idea is not without its problems as:

The lack of any obvious host galaxy for SCP 06F6 would imply either a very low black hole mass (if black holes do exist at the centres of dwarf irregular galaxies) or that the black hole has somehow been ejected from its host galaxy. While neither is impossible this does make the case for disruption by a black hole somewhat contrived.
Several new telescopes are now being designed and built that will continuously monitor the entire sky for short guest appearances of new stars, and there is no doubt that SCP 06F6 will not remain alone in puzzling astronomers over the coming years.

Astronomy – Stellar ExplosionsSupernovae, a Massive Gamma Ray Burst and a Mystery Object