Herschel spots comet massacre around nearby star

Apr 12, 2012
This image shows the infrared emission from the young star Fomalhaut and the dust disc surrounding it, as recorded with ESA's Herschel Space Observatory at a wavelength of 70 micron. To explain the emission from Fomalhaut's debris disc, astronomers invoke a steady production of dust particles via comet collisions, with an average rate of 2000 daily collisions between comets of one kilometre across or, alternatively, of 2 daily collisions between 10-kilometre-diameter comets. Credits: ESA/Herschel/PACS/Bram Acke, KU Leuven, Belgium

(Phys.org) -- ESA’s Herschel Space Observatory has studied the dusty belt around the nearby star Fomalhaut. The dust appears to be coming from collisions that destroy up to thousands of icy comets every day.

Fomalhaut is a young star, just a few hundred million years old, and twice as massive as the Sun. Its dust belt was discovered in the 1980s by the IRAS satellite, but Herschel’s new images of the belt show it in much more detail at far-infrared wavelengths than ever before.

Bram Acke, at the University of Leuven in Belgium, and colleagues analysed the Herschel observations and found the temperatures in the belt to be between –230 and –170ºC. However, because Fomalhaut is slightly off-centre and closer to the southern side of the belt, the southern side is warmer and brighter than the northern side.

Both the narrowness and asymmetry of the belt are thought to be due to the gravity of a possible planet in orbit around the star, as suggested by earlier Hubble Space Telescope images.

The Herschel data show that the dust in the belt has the thermal properties of small solid particles, with sizes of only a few millionths of a metre across.

But this created a paradox because the Hubble Space Telescope observations suggested solid grains more than ten times larger.

Those observations collected starlight scattering off the grains in the belt and showed it to be very faint at Hubble’s visible wavelengths, suggesting that the dust particles are relatively large. But that appears to be incompatible with the temperature of the belt as measured by Herschel in the far-infrared.

To resolve the paradox, Dr. Acke and colleagues suggest that the dust grains must be large fluffy aggregates, similar to dust particles released from comets in our own Solar System.  
 
These would have both the correct thermal and scattering properties. However, this leads to another problem.

The bright starlight from Fomalhaut should blow small dust particles out of the belt very rapidly, yet such grains appear to remain abundant there.

The only way to overcome this contradiction is to resupply the belt through continuous collisions between larger objects in orbit around Fomalhaut, creating new dust.

To sustain the belt, the rate of collisions must be impressive: each day, the equivalent of either two 10 km-sized comets or 2000 1 km-sized comets must be completely crushed into small fluffy, .

“I was really surprised,” says Dr. Acke, “To me this was an extremely large number.”

To keep the collision rate so high, there must be between 260 billion and 83 trillion comets in the belt, depending on their size. Our own Solar System has a similar number of comets in its Oort Cloud, which formed from objects scattered from a disc surrounding the Sun when it was as young as Fomalhaut.

“These beautiful Herschel images have provided the crucial information needed to model the nature of the dust belt around Fomalhaut,” says Göran Pilbratt, ESA Project Scientist.

Explore further: Young binary star system may form planets with weird and wild orbits

Related Stories

Herschel lives up to the family name

May 16, 2011

The Herschel Space Observatory has been observing the sky at infrared wavelengths since shortly after its launch two years ago, on 14th May 2009. But the name Herschel has a much longer legacy than that. The ...

Recommended for you

Evidence of a local hot bubble carved by a supernova

7 hours ago

I spent this past weekend backpacking in Rocky Mountain National Park, where although the snow-swept peaks and the dangerously close wildlife were staggering, the night sky stood in triumph. Without a fire, ...

Astronomers measure weight of galaxies, expansion of universe

15 hours ago

Astronomers at the University of British Columbia have collaborated with international researchers to calculate the precise mass of the Milky Way and Andromeda galaxies, dispelling the notion that the two galaxies have similar ...

Mysterious molecules in space

Jul 29, 2014

Over the vast, empty reaches of interstellar space, countless small molecules tumble quietly though the cold vacuum. Forged in the fusion furnaces of ancient stars and ejected into space when those stars ...

Comet Jacques makes a 'questionable' appearance

Jul 28, 2014

What an awesome photo! Italian amateur astronomer Rolando Ligustri nailed it earlier today using a remote telescope in New Mexico and wide-field 4-inch (106 mm) refractor. Currently the brightest comet in ...

User comments : 4

Adjust slider to filter visible comments by rank

Display comments: newest first

kevinrtrs
1 / 5 (11) Apr 12, 2012
To keep the collision rate so high, there must be between 260 billion and 83 trillion comets in the belt, depending on their size. Our own Solar System has a similar number of comets in its Oort Cloud, which formed from objects scattered from a disc surrounding the Sun when it was as young as Fomalhaut

I'm glad they put these two statements in one paragraph. They both are indications of the same problem - not enough specimens of a particular item so they have to be replenished. BUT the replenishment itself is so spectacularly unlikely that a special unobservable and never recorded source has to be invented to keep the wobbly theory from falling apart under all the contradicting OBSERVATIONS.
Just how long would it take under normal actual physical conditions for those particles to be blown away by the solar energy? Unfortunately, much too quick to make the star even 1 millions years old. And yet there it is in all it's splendor. Hence the need for the most unlikely explanations
bewertow
4 / 5 (14) Apr 12, 2012
When will you give up on your creationist trolling? You believe in a fairy tale about a magical invisible wizard who impregnated a woman with himself so he could sacrifice himself to himself in order to attone for sins that he created.

Yet you still have the balls to tell physicists with twice your IQ that they don't know what they're doing, even though you clearly have no knowledge of physics.
Eoprime
4 / 5 (4) Apr 12, 2012
pls dont feed the troll, just report him.
Maybe someday we can get rid of YECs and Crackpots
(at least in the comment section)
lbuz
4.5 / 5 (8) Apr 12, 2012
Amen with the Troll eradication. I've read PhysOrg daily for about 7 years now and never commented because there is So Much Anti-Science Crap. Rarely do I see an actual exchange of relevant and well reasoned commentary uncontaminated by uninformed, animus laden peanut gallery "I'm sooooo intelligent and perceptive that I see through to the True Nature of All Things" JABBERWOCKERY! What a waste of perfectly good bandwidth! I would dearly love to carry on conversations with people who know way more than I do, but not everything. There, I've said it.