Herschel Space Observatory discovers source of cosmic dust in a stellar explosion

Jul 07, 2011
This is an image of SN 1987A. Credit: ESA

(PhysOrg.com) -- ESA's Herschel Space Observatory is helping unravel the mystery of where cosmic dust comes from. Thanks to the resolution and sensitivity of Herschel, astronomers have been able to detect cosmic dust from a supernovae, adding weight to the theory that these cosmic fireworks are responsible for its creation.

The origin of the dust is important because it plays a crucial role in the formation of stars, particularly billions of years ago when was at its peak. Galaxies like our own Milky Way are not simply collections of stars, but also contain clouds of gas and dust, crucial to the formation of .

"Interestingly, this brand new clue does not come from observations of very distant galaxies, but from one of our closest galactic neighbours," comments Mikako Matsuura from UCL (University College London), who led a recent study published in the journal Science. Supernovae in our Galaxy are very rare, but 24 years ago astronomers were treated to one in the Large Magellanic Cloud, a small galaxy about 160,000 away.

On 23rd February 1987 the aging star could no longer support its own weight and collapsed in a violent supernova. The resulting shockwave energised material in a disc of gas and dust around the star, and is still travelling outwards at speeds of up to 6000 km/s (13 million miles per hour).

The pulse of light from the supernova lit up a ring of material almost a light year (10 million million km) across, dozens of times the size of our Solar System. This material glows in visible and ultraviolet light, as well as in . Small amounts of dust in the ring were warmed to a temperature of -100 Celsius, and this glows faintly in .

Twenty three years after the initial explosion the observed the supernova remnant. As well as the warm dust in the glowing ring, the new measurements have shown that there is dust in the centre of the remnant with a temperature of below -250 C, just 20 degrees above absolute zero. There is much more of this cold dust than the warm dust previously seen – in fact enough to form more than 200,000 Earths.

This layout compares two pictures of a supernova remnant called SN 1987A -- the left image was taken by the Herschel Space Observatory, and the right is an enlarged view of the circled region at left, taken with NASA's Hubble Space Telescope. Image credit: ESA/NASA-JPL/UCL/STScI

"We didn't expect to see SN1987A when we planned the survey," explains Margaret Meixner, from the Space Telescope Science Institute in Baltimore, USA, and who leads the HERITAGE survey for which these observations were taken. "Based on our existing knowledge of dust in supernovae, we could not have anticipated that Herschel would have detected this source. It has definitely been one of the biggest surprises of our project," she adds.

The dust was formed from material that was thrown away from the star in the initial explosion, and if similar amounts are created in all such explosions, this could explain the origin of much of the dust seen in the .

"Since no facility comparable to Herschel has existed during the past two decades, we cannot say for certain large amount of cold dust was produced," notes Matsuura. "But we have proved that a supernova can produce an amount of dust comparable to the mass of the Sun over a period of, at most, a couple of dozen years—a blink of an eye with respect to a star's lifetime," she adds.

The observations of SN1978a are crucial for understanding the remnants of supernova that Herschel is observing in our own Galaxy, which exploded hundreds or thousands of years ago. But this latest result also has much further reaching consequences. "With objects like SN1987a, we can investigate details that are almost impossible to discern in supernovae inside more distant galaxies. This helps us improve our understanding of these stellar explosions, which we can then apply to the broader context of galaxy evolution," explained Matsuura.

Most of the galaxies seen in the very distant Universe appear bright in the far-infrared as seen by Herschel, but very faint in visible light. This is because they contain large quantities of dust, which blocks most of the visible light from the stars in the galaxies, and these observations by Herschel of SN1987a help to explain where most of that dust comes from. Astronomers are very interested in this because these galaxies are seen as they were 8-10 billion years ago, a period in the Universe when stars were forming at rates higher than ever before or since.

These observation show the power of Herschel for investigating the origin of dust across the ages, from our own Galactic neighbourhood to galaxies in the distant Universe", remarked Matt Griffin, from Cardiff University and principal investigator of the SPIRE instrument. "In turn, this is helping us understand the formation of the stars we see today".

Explore further: Image: Multicoloured view of supernova remnant

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User comments : 6

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fuviss_co_uk
not rated yet Jul 07, 2011
hmmm. This was quite obvious
david_42
not rated yet Jul 07, 2011
"On 23rd February 158013 BCE the aging star could no longer support its own weight and collapsed in a violent supernova."

Fixed that for you.
Caliban
5 / 5 (4) Jul 07, 2011
What? No mention of a neutron-star supernova core, energetically creating and shedding a solar atmosphere via the process of neutron-repulsion?
yyz
not rated yet Jul 08, 2011
The Matsuura et al paper mentioned in this article is available here: http://arxiv.org/...1477.pdf

Besides deriving the spectral energy distribution(SED) for this SN remnant, observations from Spitzer, Herschel & submm telescopes are compared to deduce the nature of the central region of SN1987A (See Fig 2).

Also, no observations of radioactive Ni-56, Ti-44 or Co-60 are found in the *cold* dust surrounding the object at the center of SN1978A. The researchers note that x-ray emission from the nearby collisional ring are probably responsible for the observed 20K temperature of the central object in SN1987A

How would neutron repulsion explain these observations, as the heaviest metals (like Ni-56, Ti-44 & Co-60) should be found very close to the compact object at the center of this SNR?

yyz
not rated yet Jul 09, 2011
A second observation of SN 1987A in the submillimeter using APEX has also been published: http://arxiv.org/...23v1.pdf

Haven't had time to more than skim them as yet, but the preliminary submm observations see a predicted cloud of cold dust that extends out further than that seen by shorter wavelength Herschel observations and may be related to outflows when in it's red giant phase.
yyz
not rated yet Jul 09, 2011
These new observations in FIR, submillimeter & millimeter are in good agreement with observations by Chevalier of a shell 4.5pc from the progenitor, presumably resulting from interactions with the stellar wind from the RSG precursor and the surrounding medium: http://articles.a...ype=.pdf

NIR observations by Spitzer reveal 10E-6 solar masses of dust at 180K in the rings encircling SN1987A while Herschel finds ~1 solar mass of dust created in the close vicinity of the central compact object, with a temperature of 20K (this meager heating of this inner dust could be due to XR emission from the collisional ring).

The large amount of dust inferred to be present in the ejecta of SN1987A is consistent to that required to explain the dust masses in hi-z galaxies (~0.1-1 solar masses of dust per SN). SNe may play a large role in dust production in galaxies.

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