New class of stellar explosions discovered

Jun 08, 2011 by Marcus Woo
The 1.2-meter Samuel Oschin Telescope at Palomar Observatory that was used to discover four supernovae of a new class. Inset: one of the newly discovered supernovae, PTF09cnd. Credit: Caltech/Scott Kardel/Robert Quimby/modified from Nature

They're bright and blue-and a bit strange. They're a new type of stellar explosion that was recently discovered by a team of astronomers led by the California Institute of Technology (Caltech). Among the most luminous in the cosmos, these new kinds of supernovae could help researchers better understand star formation, distant galaxies, and what the early universe might have been like.

"We're learning about a whole new class of that wasn't known before," says Robert Quimby, a Caltech postdoctoral scholar and the lead author on a paper to be published in the June 9 issue of the journal Nature. In addition to finding four explosions of this type, the team also discovered that two previously known supernovae, whose identities had baffled astronomers, also belonged to this new class.

Quimby first made headlines in 2007 when-as a graduate student at the University of Texas, Austin-he discovered what was then the brightest supernova ever found: 100 billion times brighter than the sun and 10 times brighter than most other supernovae. Dubbed 2005ap, it was also a little odd. For one thing, its spectrum-the that tells astronomers what the supernova is made of, how far away it is, and what happened when it blew up-was unlike any seen before. It also showed no signs of hydrogen, which is commonly found in most supernovae.

At around the same time, astronomers using the discovered a mysterious supernova called SCP 06F6. This supernova also had an odd spectrum, though there was nothing that indicated this cosmic blast was similar to 2005ap.

Shri Kulkarni, Caltech's John D. and Catherine T. MacArthur Professor of Astronomy and and a coauthor on the paper, recruited Quimby to become a founding member of the Palomar Transient Factory (PTF). The PTF is a project that scans the skies for flashes of light that weren't there before-flashes that signal objects called transients, many of which are supernovae. As part of the PTF, Quimby and his colleagues used the 1.2-meter Samuel Oschin Telescope at Palomar Observatory to discover four new supernovae. After taking spectra with the 10-meter Keck telescopes in Hawaii, the 5.1-meter telescope at Palomar, and the 4.2-meter William Herschel Telescope in the Canary Islands, the astronomers discovered that all four objects had an unusual spectral signature.

Quimby then realized that if you slightly shifted the spectrum of 2005ap-the supernova he had found a couple of years earlier-it looked a lot like these four new objects. The team then plotted all the spectra together. "Boom-it was a perfect match," he recalls.

The astronomers soon determined that shifting the spectrum of SCP 06F6 similarly aligned it with the others. In the end, it turned out that all six supernovae are siblings, and that they all have spectra that are very blue-with the brightest wavelengths shining in the ultraviolet.

According to Quimby, the two mysterious supernovae-2005ap and SCP 06F6-had looked different from one another because 2005ap was 3 billion light-years away while SCP 06F6 was 8 billion light-years away. More distant supernovae have a stronger cosmological redshift, a phenomenon in which the expanding universe stretches the wavelength of the emitted light, shifting supernovae spectra toward the red end.

The four supernovae discovered by the Palomar Transient Factory. Left: before explosion. Right: after explosion. From top to bottom, the supernovae are PTF09atu, PTF09cnd, PTF09cwl, and PTF10cwr. Credit: Caltech/Robert Quimby/Nature

The four new discoveries, which had features similar to 2005ap and SCP 06F6, were at an intermediate distance, providing the missing link that connected the two previously unexplained supernovae. "That's what was most striking about this-that this was all one unified class," says Mansi Kasliwal, a Caltech graduate student and coauthor on the Nature paper.

Even though astronomers now know these supernovae are related, no one knows much else. "We have a whole new class of objects that can't be explained by any of the models we've seen before," Quimby says. What we do know about them is that they are bright and hot-10,000 to 20,000 degrees Kelvin; that they are expanding rapidly at 10,000 kilometers per second; that they lack hydrogen; and that they take about 50 days to fade away-much longer than most supernovae, whose luminosity is often powered by radioactive decay. So there must be some other mechanism that's making them so bright.

One possible model that would create an explosion with these properties involves a pulsating star about 90 to 130 times the mass of the sun. The pulsations blow off hydrogen-free shells, and when the star exhausts its fuel and explodes as a supernova, the blast heats up those shells to the observed temperatures and luminosities.

A second model requires a star that explodes as a supernova but leaves behind what's called a magnetar, a rapidly spinning dense object with a strong magnetic field. The rotating magnetic field slows the magnetar down as it interacts with the sea of charged particles that fills space, releasing energy. The energy heats the material that was previously blown off during the supernova explosion and can naturally explain the brightness of these events.

The newly discovered supernovae live in dim, small collections of a few billion stars called dwarf galaxies. (Our own Milky Way has 200-400 billion stars.) The supernovae, which are almost a hundred times brighter than their host galaxies, illuminate their environments like distant street lamps lighting up dark roads. They work as a kind of backlight, enabling astronomers to measure the spectrum of the interstellar gas that fills the dwarf galaxies in which the supernovae reside, and revealing each galaxy's composition. Once an observed supernova fades a couple of months later, astronomers can directly study the dwarf galaxy-which would have remained undetected if it weren't for the supernova.

These supernovae could also reveal what ancient stars might have been like, since they most likely originate from stars around a hundred times more massive than the sun-stars that would have been very similar to the first stars in the universe.

"It is really amazing how rich the night sky continues to be," Kulkarni says. "In addition to supernovae, the Palomar Transient Factory is making great advances in stellar astronomy as well."

Explore further: Quest for extraterrestrial life not over, experts say

More information: "A new class of hydrogen-poor super-luminous stellar explosions" Nature (2011).

Related Stories

Stellar Explosion Displays Massive Carbon Footprint

Jun 01, 2009

(PhysOrg.com) -- While humans are still struggling to get rid of unwanted carbon it appears that the heavens are really rather good at it. New research by astrophysicists at the University of Warwick has discovered that a ...

Star Light, Star Bright, Its Explanation is Out of Sight

Jan 06, 2009

(PhysOrg.com) -- A mysterious flash of light from somewhere near or far in the universe is still keeping astronomers in the dark long after it was first detected by NASA's Hubble Space Telescope in 2006. It ...

Unique sky survey brings new objects into focus

Jun 15, 2009

An innovative sky survey has begun returning images that will be used to detect unprecedented numbers of powerful cosmic explosions-called supernovae-in distant galaxies, and variable brightness stars in our ...

Recommended for you

Quest for extraterrestrial life not over, experts say

22 hours ago

The discovery of an Earth-sized planet in the "habitable" zone of a distant star, though exciting, is still a long way from pointing to the existence of extraterrestrial life, experts said Friday. ...

Continents may be a key feature of Super-Earths

Apr 18, 2014

Huge Earth-like planets that have both continents and oceans may be better at harboring extraterrestrial life than those that are water-only worlds. A new study gives hope for the possibility that many super-Earth ...

Exoplanets soon to gleam in the eye of NESSI

Apr 18, 2014

(Phys.org) —The New Mexico Exoplanet Spectroscopic Survey Instrument (NESSI) will soon get its first "taste" of exoplanets, helping astronomers decipher their chemical composition. Exoplanets are planets ...

User comments : 12

Adjust slider to filter visible comments by rank

Display comments: newest first

El_Nose
5 / 5 (2) Jun 08, 2011
with no mention of the elements found in their spectrum ... sigh

so what say you oh guru of nuetron repulsion?
omatumr
1 / 5 (7) Jun 08, 2011
with no mention of the elements found in their spectrum ... sigh

so what say you oh guru of nuetron repulsion?


Most stellar explosions are probably powered by neutron repulsion in the core.

That blows away the material that accumulated above, exposing the neutron star.

The spectrum would show the material that blew away.

With kind regards,
Oliver K. Manuel
yyz
5 / 5 (1) Jun 08, 2011
SCP 06F6 is a fascinating object in itself, having a rise time to max light of ~100 days, as noted in the 2008 discovery paper by Barbary et al: http://arxiv.org/...9.1648v1

The 2008 paper discusses some interpretations of the 5 observed broad absorption bands seen in the 400-650nm region of the optical spectra, especially wrt the distance to the object.

That being said, a recent paper by Chatzopoulos, Wheeler & Vinko propose a redshift of z=0.57. From the abstract:

"We suggest that a model of SCP06F6 worth futher exploration is one in which the redshift is $\sim$ 0.57, the spectral features are Ca and iron peak elements, and the light curve is powered by the diffusive release of a substantial amount of energy from nickel decay or from an energetic supernova buried in the ejecta of an LBV-like event."

Fig 1 of the paper presents VLT & Subaru spectra, along with modeled spectra and other SNe spectra adjusted to a redshift z=0.57: http://arxiv.org/...9.1798v2

Decimatus
not rated yet Jun 08, 2011
Wouldn't neutron cores leave a much more massive star than would otherwise be apparent? For instance the Sun. Wouldn't the outer layers of the star need to be less denese to account for the extra mass at the core?

Or, if each star is actually much more massive than we give it credit, would that also soak up some additional mass in the dark materr/energy ratio?

Could there be any kind of neutron core, however small, in Jupiter? Or even the earth?

What kind of characteristics would a neutron star have that would be right on the edge of black hole territory. For instance, just under the mass to create an event horizon effect, yet massive enough to have some of those properties some of the time or in localized areas?

Could there be stars out there that have event horizons on the inside, and yet not strong enough to compress or destroy the piled up matter on the outside of the star?
yyz
5 / 5 (4) Jun 08, 2011
"Most stellar explosions are probably powered by neutron repulsion in the core.

That blows away the material that accumulated above, exposing the neutron star."

It's now been 24 years since SN 1987A erupted. Where is this neutron star that's blown away accumulated material in this recent HST image: http://cdn.physor...nova.jpg

There's no sign of a neutron star in this system at radio and X-ray wavelengths either.

What gives? :^)

With kind regards,
Jon C. Hanford
jamesrm
not rated yet Jun 09, 2011
http://en.wikiped..._star.3F
Missing neutron star?
SN 1987A appears to be a core-collapse supernova, which should result in a neutron star. Indeed, the neutrino data indicate that a compact object did form at the star's core. However, since the supernova first became visible, astronomers have been searching for the collapsed core but have not detected it. The Hubble Space Telescope has taken images of the supernova regularly since August 1990, but, so far, the images have shown no evidence of a neutron star. A number of possibilities for the 'missing' neutron star are being considered, although none is clearly favored. The first is that the neutron star is enshrouded in dense dust clouds so that it cannot be seen. Another is that a pulsar was formed, but with either an unusually large or small magnetic field.

astro_optics
1 / 5 (1) Jun 09, 2011
Any chance it could be exploding black holes after they lose enough mass so they stop being black holes... crazy idea ha? They'd have to be in a fairly void space so the amount of incoming energy/mass would be less that the amount lost...
Kedas
1 / 5 (1) Jun 09, 2011
Some intelligent race probably found a much better way to destroy themselves or they are trying to get our attention ;)
vidar_lund
not rated yet Jun 09, 2011
Any chance it could be exploding black holes after they lose enough mass so they stop being black holes... crazy idea ha? They'd have to be in a fairly void space so the amount of incoming energy/mass would be less that the amount lost...

No, black hole evaporation is only predicted for tiny black holes and the final contraction would be more like a small puff than a big blast.
Mahal_Kita
not rated yet Jun 09, 2011
We're still making baby steps forward in the realms of physics and astronomy. Still discovering that we have so much to discover still. It's a thrill to be alive in this era of progress..
omatumr
2 / 5 (2) Jun 09, 2011
We're still making baby steps forward in the realms of physics and astronomy. Still discovering that we have so much to discover still. It's a thrill to be alive in this era of progress..


I agree completely.

Oliver K. Manuel
Former NASA Principal
Investigator for Apollo
yyz
5 / 5 (3) Jun 09, 2011
@jamesrm,

"A number of possibilities for the 'missing' neutron star are being considered, although none is clearly favored. The first is that the neutron star is enshrouded in dense dust clouds so that it cannot be seen. Another is that a pulsar was formed, but with either an unusually large or small magnetic field."

The formation of a black hole remnant has been discussed. It has also been proposed that the remnant of SN1987A might be a strange quark star: http://iopscience..._732.pdf

Whatever type of remnant was produced (or possibly none at all!), it should greatly add to our knowledge of supernovae formation and evolution, just like the distant events discussed in this article.

More news stories

Sun emits a mid-level solar flare

The sun emitted a mid-level solar flare, peaking at 9:03 a.m. EDT on April 18, 2014, and NASA's Solar Dynamics Observatory captured images of the event. Solar flares are powerful bursts of radiation. Harmful ...

Airbnb rental site raises $450 mn

Online lodging listings website Airbnb inked a $450 million funding deal with investors led by TPG, a source close to the matter said Friday.

Health care site flagged in Heartbleed review

People with accounts on the enrollment website for President Barack Obama's signature health care law are being told to change their passwords following an administration-wide review of the government's vulnerability to the ...