Featured Research

from universities, journals, and other organizations

Fermi satellite detects gamma-rays from exploding novae: Surprising discovery dispels long-held idea

Date:
July 31, 2014
Source:
Arizona State University
Summary:
Astronomers have discover very high energy gamma rays being emitted by an exploding star. The surprising discovery dispels the long-held idea that classical nova explosions are not powerful enough to produce such high-energy radiation.

This picture is an artist's conception of the explosion of V407 Cyg. It shows the white dwarf exploding inside the outer layers of its nearby companion star.
Credit: Photo by: (c) David A. Hardy/astroart.org

The Universe is home to a variety of exotic objects and beautiful phenomena, some of which can generate almost inconceivable amounts of energy. ASU Regents' Professor Sumner Starrfield is part of a team that used the Large Area Telescope (LAT) onboard NASA's Fermi Gamma-ray Space Telescope satellite to discover very high energy gamma rays (the most energetic form of light) being emitted by an exploding star. The surprising discovery dispels the long-held idea that classical nova explosions are not powerful enough to produce such high-energy radiation.

In March 2010, scientists using the LAT reported a surprising discovery: detection of gamma rays that appeared to come from a nova, V407 Cygni. The LAT, in orbit around the Earth, views ∼20% of the sky instantaneously and the entire sky every three hours. It is the most sensitive gamma-ray space telescope ever flown.

A nova is observed as a sudden, short-lived rapid increase in the brightness of an otherwise inconspicuous star. It results from runaway thermonuclear explosions that typically take place in a binary system on the surface of a white dwarf fueled by mass from a companion star. The outburst occurs when a white dwarf erupts in an enormous thermonuclear explosion. The explosion is equivalent to about 100,000 times the energy that the sun gives off every year. Unlike supernovas, novae do not result in the destruction of their stars.

Although novae produce bright optical events, they had not previously been considered as potential sources of high energy gamma rays since they are not predicted to accelerate particles to the required energies (very nearly the speed of light). Few cosmic marvels can accelerate particles to the energies required to generate gamma rays, billions of times more energetic than the type of light visible to our eyes. Researchers had expected and seen X-rays from the resulting waves of expanding gas in prior novae.

The finding overturned the notion that novae explosions lack the power to emit such high-energy radiation. Subsequently in June 2012, two more novae were detected with the LAT, Nova Sco 2012 and Nova Mon 2012, thus heralding novae as a new gamma-ray source class.

These findings are published in the August 1 issue of the journal Science with Teddy Cheung, an astrophysicist at the Naval Research Laboratory in Washington, as the lead author.

"This was a completely unexpected discovery and we still don't understand the cause," says computational astrophysicist Starrfield, a professor in the School of Earth and Space Exploration at ASU. "No one suspected novae were violent enough to be emitting at these very high energies. However, it now seems possible that a signification fraction -- near 100% -- of novae are gamma ray sources."

Origins unknown

The white dwarf star V407 Cyg lies 9,000 light-years away in the plane of our Milky Way galaxy. It erupted in a rare type of nova called a likely recurrent symbiotic nova, in which the companion star is a pulsating red giant star (about 500 times the size of the sun) blowing out a strong stellar wind. The explosion of the white dwarf occurs inside the atmosphere of the companion star.

Researchers suggested that the gamma rays in the nova were generated when the blast waves from the nova collided with the very dense winds from the red giant, something that doesn't appear in classical novae.

Although the LAT followed up on later optically bright classical novae, it saw nothing for two years, and the theory that V407 Cyg was a special case seemed confirmed. Then, in June 2012, two separate novae were seen in gamma rays: Nova Sco 2012 and Nova Mon 2012 both emitted detectable levels of gamma rays.

But Nova Sco 2012 and Nova Mon 2012 are classical novae accreting from small, nearby companions. There's no thick stellar wind to produce a shock like there is in V407 Cyg. So where are the gamma rays coming from?

The answer at the moment is: We don't know.

Although researchers can't yet explain how and why, what we do know is that novae can be gamma ray emitters and they are not as rare as originally suspected.

"We are puzzled and ongoing studies of possible causes are underway via computer modeling of the events," says Starrfield. "This exciting discovery is telling us something important about the explosions of classical novae but we don't, as yet, know what it means."


Story Source:

The above story is based on materials provided by Arizona State University. Note: Materials may be edited for content and length.


Journal Reference:

  1. The Fermi-LAT Collaboration. Fermi establishes classical novae as a distinct class of gamma-ray sources. Science, 2014 DOI: 10.1126/science.1253947

Cite This Page:

Arizona State University. "Fermi satellite detects gamma-rays from exploding novae: Surprising discovery dispels long-held idea." ScienceDaily. ScienceDaily, 31 July 2014. <www.sciencedaily.com/releases/2014/07/140731150043.htm>.
Arizona State University. (2014, July 31). Fermi satellite detects gamma-rays from exploding novae: Surprising discovery dispels long-held idea. ScienceDaily. Retrieved September 19, 2014 from www.sciencedaily.com/releases/2014/07/140731150043.htm
Arizona State University. "Fermi satellite detects gamma-rays from exploding novae: Surprising discovery dispels long-held idea." ScienceDaily. www.sciencedaily.com/releases/2014/07/140731150043.htm (accessed September 19, 2014).

Share This



More Space & Time News

Friday, September 19, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

MIT BioSuit A New Take On Traditional Spacesuits

MIT BioSuit A New Take On Traditional Spacesuits

Newsy (Sep. 19, 2014) The MIT BioSuit could be an alternative to big, bulky traditional spacesuits, but the concept needs some work. Video provided by Newsy
Powered by NewsLook.com
Boeing, SpaceX to Send Astronauts to Space Station

Boeing, SpaceX to Send Astronauts to Space Station

AFP (Sep. 17, 2014) NASA selected Boeing and SpaceX on Tuesday to build America's next spacecraft to carry astronauts to the International Space Station (ISS) by 2017, opening the way to a new chapter in human spaceflight. Duration: 01:13 Video provided by AFP
Powered by NewsLook.com
East Coast Treated To Rare Meteor Sighting

East Coast Treated To Rare Meteor Sighting

Newsy (Sep. 16, 2014) Numerous residents along the East Coast reported seeing a bright meteor flash through the sky Sunday night. Video provided by Newsy
Powered by NewsLook.com
Space Race Pits Bezos Vs Musk

Space Race Pits Bezos Vs Musk

Reuters - Business Video Online (Sep. 16, 2014) Amazon CEO Jeff Bezos' startup will team up with Boeing and Lockheed to develop rocket engines as Elon Musk races to have his rockets certified. Fred Katayama reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins