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Nearby supernova may illuminate dark energy puzzle

ptf11kly_arrow-350.jpgA Type Ia supernova, the brightest and most energetic kind of stellar explosion – and the type that astronomers use to measure the accelerating expansion of the universe – has been spotted in a nearby galaxy, making it the closest such event in nearly 40 years.

Astronomers working with the Palomar Transient Factory (PTF), an automated sky survey based at the Mount Palomar observatory in California say their robotic telescope detected the new supernova (arrow) on 23 August in the galaxy M101 located some 21 million light years away.

“We are very excited to get one this close,” says Oxford University astronomer and PTF collaborator Mark Sullivan. “We essentially discovered it the day it blew up.”

The early detection, coupled with the supernova’s relative nearness (in cosmic terms) creates a rare opportunity for researchers trying to refine their understanding of an important class of stellar explosion. In the coming hours and days telescopes on the ground and in space, including the Hubble Space Telescope, and at the Keck Observatory on Mauna Kea, Hawaii, will be swiveling over to gather data from the rapidly brightening object.

“We know it’s the youngest Type Ia ever observed,” says Peter Nugent of Lawrence Berekely National Laboratory in Berkeley, California, who leads the Type Ia search group with PTF. “This thing just shot up out of nowhere.”

Now the race is on to accumulate as much data as possible and as quickly as possible, says Nugent. This will help clarify what goes on in the earliest stages of a Type 1a supernova, when most of the light is emanating from the outermost layers of the exploding star. “At this early epoch, the supernova can change hour to hour,” he says.

A thorough set of observations could catapult this supernova into the ranks of those few textbook cases that are used by astronomers as callibration tools for distance measurements.

Unlike other kinds of supernovae, triggered when massive stars undergo core collapse, Type Ias are produced when white dwarf stars are pushed over a theoretical mass limit. The result is a thermonuclear detonation with a well predicted peak brightness, which makes such events ideal ‘standard candles’ for measuring extragalactic distances. Observations of Type Ia supernovae in remote galaxies led to the surprising revelation in 1998 that the expansion of the universe is speeding up over time due to the presence of dark energy, a poorly understood phenomenon. Subsequent studies have helped confirm dark energy’s fundamental role in shaping the cosmos, but the picture depends on astronomers’ understanding of how Type Ia supernovae shine. Unknown factors in the physics of Type Ias may have a bearing on the way they are used to calculate precise distances.


“One of the biggest unknowns is the effect of metalicity,” says Sullivan. Metallicity is a measure of a star’s accumulation of heavier elements relative to its hydrogen. If the star goes supernova, its metalicity may influence how bright the explosion ultimately appears. Among the observations planned for the new supernova are spectroscopic studies across a broad range of wavelengths, Sullivan says, particularly in the very early stages of the explosion, “when the effects of metalicity are most profound.”

Sullivan predicts that by the time the supernova peaks in early September it will have a visual magnitude of 9-10, placing it within reach of observers using small telescopes or binoculars under clear, dark skies.

M101, better known as ‘the Pinwheel Galaxy’ because of its striking spiral form, is a popular target for astrophotographers. Its location in the northern constellation of Ursa Major (just above the handle of the Big Dipper, or the Plough) virtually guarantees that the supernova will be frequently imaged by amateur astronomers in Europe, the United States and Japan over the next few weeks and followed closely – potentially for years – as its luminosity gradually diminishes.

Although there has not been a Type Ia supernova as near as this since 1972, the modern record holder for all supernovae types remains SN1987a, which exploded in the Large Magellanic Cloud, a satellite system of the Milky Way, in February 1987 and was visible to the naked eye. A supernova has not been seen exploding within our own galaxy since 1604.

Image: Peter Nugent, Palomar Transient Factory

Comments

  1. Report this comment

    James T. Dwyer said:

    The article states:

    ““One of the biggest unknowns is the effect of metalicity,” says Sullivan. Metallicity is a measure of a star’s accumulation of heavier elements relative to its hydrogen. If the star goes supernova, its metalicity may influence how bright the explosion ultimately appears.”

    As I understand, it’s been presumed that the peak emission luminosity of all type Ia SNe are consistent, allowing it to be used as a standard candle. If metallicity alters the peak emission luminosity of type Ia SNe and their metallacity is increasing over time, more distant type Ia SNe peak period emission luminosity would not be directly comparable to nearer type Ia SNe.

    If that is the case, as I understand, the observational studies that established that the expansion of the universe is accelerating might be invalidated.

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    Dax Hart said:

    Comet Elenin will be affected by phantom energy forces so Earth scientists need to UNITE to determine October 2011 NEO damage. 22million – 21 million = 1 million miles apart = definate altering of course for Elenin & other Orbiters which will cause Global Event Horizons I have indicated this for years gravity = push, Higgs NOT found = 5th dimensional, time travel both ways possible, Time is illusion, Universal constants not reliable ie expansion rate, new model physics as current is 3 dimentional biolimited.

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    Robert L. Oldershaw said:

    In the latest issue of Science 8/26/11 there is a report by Bailes et al describing the discovery and properties of a new pulsar-planet system, the third so far.

    Pulsar-planets were first discovered in 1992.

    In 1989, in the International Journal of Theoretical Physics, vol. 28, No. 12, pp. 1503-1532, it was definitively predicted by a new paradigm called the self-similar cosmological paradigm (now referred to as Discrete Scale Relativity) that planetary-mass objects would be discovered orbiting stellar-mass ultracompact objects.

    Discrete Scale Relativity was the only theory to ever definitively predict systems like pulsar-planets, explain how they form, and explain why they should not be unusually rare objects.

    If you would like to read more about this definitive scientific prediction by Discrete Scale Relativity, see Selected Paper #4 at http://www3.amherst.edu/~rloldershaw , which was also published in IJTP.

    It will be most interesting to see the more detailed properties of this system once further research is done on it, especially with the new Russian Spektr-R radio wave satellite that can be linked to Earth-based radio telescopes to give unprecedented resolution of radio sources, like a pulsar-planet system.

    Game On!

    RLO

    Fractal Cosmology

  4. Report this comment

    DavidMcC said:

    James, maybe what they have shown here is that a type 1a supernova has to peak before it can be used as a standard candle.

  5. Report this comment

    James T. Dwyer said:

    David – yes, as I understand, it is the presumed consistency of their peak period emission luminosity that allows their use as a standard candle. The article states: “its metalicity may influence how bright the explosion ultimately appears.” I interpret that to mean that metalicity may effect the peak period emission luminosity, making it inconsistent.

    If that is the case, the unexpectedly high peak emission luminosity of higher-z type Ia SNe identified in the studies concluding that expansion of the universe is accelerating may have actually been the product of decreasing luminosity as metalicity generally increases in the temporally developing universe. The more ancient high-z peak emissions of distant type Ia SNe may have been brighter because of generally lower metalicity in the earlier universe.

  6. Report this comment

    James Dwyer said:

    As a layperson, I understand that, at peak luminosity, type Ia SNe are primarily burning “intermediate-mass elements from oxygen to calcium”. If lower metalicity in the early universe meant that the matter accreted by a white dwarf (for example) from a companion massive star was composed of lower mass elements that produced greater peak emission luminosities, it should be determinable by comparing the spectroscopic characteristics of near and far type Ia SNe. Perhaps this has already been determined?

    As stated in http://en.wikipedia.org/wiki/Type_Ia_Supernova#Light_curve
    “Type Ia supernovae have a characteristic light curve, their graph of luminosity as a function of time after the explosion. Near the time of maximum luminosity, the spectrum contains lines of intermediate-mass elements from oxygen to calcium; these are the main constituents of the outer layers of the star.”

  7. Report this comment

    David Whitlock said:

    Metallicity is likely to be a small, second order factor in the light curve, mostly relating to ionization and optical depth in the expanding plasma and not to total energy release.

    They are talking about looking at very early changes in light emission, those are due to the composition of the outer layers and how they become transparent.

    1. Report this comment

      James Dwyer said:

      Your assessment seems to contradict some of the statements made in the article, including:

      “One of the biggest unknowns is the effect of metalicity,” says Sullivan. Metallicity is a measure of a star’s accumulation of heavier elements relative to its hydrogen. If the star goes supernova, its metalicity may influence how bright the explosion ultimately appears. Among the observations planned for the new supernova are spectroscopic studies across a broad range of wavelengths, Sullivan says, particularly in the very early stages of the explosion, “when the effects of metalicity are most profound.”

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