Debris disk

Hubble Space Telescope observation of the debris ring around Fomalhaut. The inner edge of the disk may have been shaped by the orbit of Fomalhaut b, at lower right.

A debris disk is a circumstellar disk of dust and debris in orbit around a star. Sometimes these disks contain prominent rings, as seen in the image of Fomalhaut on the right. Debris disks have been found around both evolved and young stars, as well as at least one debris disk in orbit around a neutron star.^[1] They can constitute a phase in the formation of a planetary system following the protoplanetary disk phase.^[2] They can also be produced and maintained as the remnants of collisions between planetismals.^[3]

By 2001, over 900 candidate stars had been found to possess a debris disk. They are usually located by examining the star system in infrared light and looking for an excess of radiation beyond that emitted by the star. This excess is inferred to be radiation from the star that has been absorbed by the disk, then radiated away as infrared energy.^[4]

Debris disks are often described as massive analogs to the debris in the Solar System. Most known debris disks have radii of 10–100 astronomical units (AU); they resemble the Kuiper belt in the Solar System, but with much more dust. Some debris disks contain a component of warmer dust located within 10 AU from the central star. This dust is sometimes called exozodiacal dust by analogy to zodiacal dust in the Solar System.

Observation history

In 1984 a debris disk was detected around the star Vega using the IRAS satellite. Initially this was believed to be a protoplanetary disk, but it is now thought to be a debris disk due to the lack of gas in the disk and the age of the star. Subsequently irregularities have been found in the disk, which may be indicative of the presence of planetary bodies.^[5] Similar discoveries of debris disks were made around the stars Fomalhaut and Beta Pictoris.

The nearby star 55 Cancri, a system that is also known to contain five planets, was reported to also have a debris disk,^[6] but that detection could not be confirmed.^[7] Structures in the debris disk around Epsilon Eridani suggest perturbations by a planetary body in orbit around that star, which may be used to constrain the mass and orbit of the planet.^[8]

Origin

During the formation of a Sun-like star, the object passes through the T-Tauri phase during which it is surrounded by a disk-shaped nebula. Out of this material are formed planetesimals, which can undergo an accretion process to form planets. The nebula continues to orbit the pre-main-sequence star for a period of 1–20 million years until it is cleared out by radiation pressure. Additional dust may then be generated about the star by collisions between the planetismals, which forms a disk out of the resulting debris. At some point during their lifetime, about 45% of these stars are surrounded by a debris disk, which then can be detected by the thermal emission of the dust using an infrared telescope. Repeated collisions can cause a disk to persist for much of the lifetime of a star.^[9]

Typical debris disks contain small grains 1–100 μm in size. Collisions will grind down these grains to sub-micrometre sizes, which will be removed from the system by radiation pressure from the host star. In very tenuous disks like the ones in the Solar System, the Poynting–Robertson effect can cause particles to spiral inward instead. Both processes limit the lifetime of the disk to 10 Myr or less. Thus, for a disk to remain intact, a process is needed to continually replenish the disk. This can occur, for example, by means of collisions between larger bodies, followed by a cascade that grinds down the objects to the observed small grains.^[10]

For collisions to occur in a debris disk, the bodies must be gravitationally perturbed sufficiently to create relatively large collisional velocities. A planetary system around the star can cause such perturbations, as can a binary star companion or the close approach of another star.^[10] The presence of a debris disk may indicate a high likelihood of terrestrial planets orbiting the star.^[11]

Known belts

Belts of dust or debris have also been detected around stars other than the Sun, including the following:

Star	Spectral class[12]	Distance (ly)	Orbit (AU)	Notes
Epsilon Eridani	K2V	10.5	35–75	[8]
Tau Ceti	G8V	11.9	35–50	[13]
Vega	A0V	25	86–200	[5][14]
Fomalhaut	A3V	25	133–158	[5]
AU Microscopii	M1Ve	33	50–150	[15]
HD 69830	K0V	41	<1	[16]
55 Cancri A	G8V	41	27–50	[6]
Pi1 Ursae Majoris	G1.5Vb	46.5	?	[17]
HD 207129	G0V	52	148–178	[18]
HD 139664	F5IV–V	57	60–109	[19]
Eta Corvi	F2V	59	100–150	[20]
HD 53143	K1V	60	?	[19]
Beta Pictoris	A6V	63	25–550	[14]
Zeta Leporis	A2Vann	70	2–8	[21]
HD 92945	K1V	72	45–175	[22]
HD 107146	G2V	88	130	[23]
HR 8799	A5V	129	75	[24]
51 Ophiuchi	B9	131	0.5–1200	[25]
HD 12039	G3–5V	137	5	[26]
HD 98800	K5e (?)	150	1	[27]
HD 15115	F2V	150	315–550	[28]
HR 4796 A	A0V	220	200	[29][30]
HD 141569	B9.5e	320	400	[30]
HD 113766 A	F4V	430	0.35–5.8	[31]

The orbital distance of the belt is an estimated mean distance or range, based either on direct measurement from imaging or derived from the temperature of the belt. The Earth has an average distance from the Sun of 1 AU.

See also

• Accretion disc
• Asteroid belt
• Protoplanetary disk

References

1. ^ Wang, Z.; Chakrabarty, D.; Kaplan, D. L. (2006). "A debris disk around an isolated young neutron star". Nature 440 (7085): 772–775. arXiv:astro-ph/0604076. Bibcode 2006astro.ph..4076W. doi:10.1038/nature04669. PMID 16598251. 
2. ^ "Spitzer Team Says Debris Disk Could Be Forming Infant Terrestrial Planets". NASA. 2005-12-14. Archived from the original on 2006-09-08. http://web.archive.org/web/20060908075059/http://www.spitzer.caltech.edu/Media/happenings/20051214/. Retrieved 2007-01-03. 
3. ^ "Spitzer Sees Dusty Aftermath of Pluto-Sized Collision". NASA. 2005-01-10. Archived from the original on 2006-09-08. http://web.archive.org/web/20060908075059/http://www.spitzer.caltech.edu/Media/happenings/20051214/. Retrieved 2007-01-03. 
4. ^ "Debris Disk Database". Royal Observatory Edinburgh. http://www.roe.ac.uk/ukatc/research/topics/dust/identification.html. Retrieved 2007-01-03. 
5. ^ ^{a b c} "Astronomers discover possible new Solar Systems in formation around the nearby stars Vega and Fomalhaut" (Press release). Joint Astronomy Centre. 1998-04-21. http://outreach.jach.hawaii.edu/pressroom/1998_vega/. Retrieved 2006-04-24. 
6. ^ ^{a b} "University Of Arizona Scientists Are First To Discover Debris Disk Around Star Orbited By Planet". ScienceDaily. 1998-10-03. http://www.sciencedaily.com/releases/1998/10/981023073211.htm. Retrieved 2006-05-24. 
7. ^ Schneider, G.; Becklin, E. E.; Smith, B. A.; Weinberger, A. J.; Silverstone, M.; Hines, D. C. (2001). "NICMOS Coronagraphic Observations of 55 Cancri". The Astronomical Journal 121 (1): 525. arXiv:astro-ph/0010175. Bibcode 2001AJ....121..525S. doi:10.1086/318050. 
8. ^ ^{a b} Greaves, J. S.; Holland, W. S.; Wyatt, M. C.; Dent, W. R. F.; Robson, E. I.; Coulson, I. M.; Jenness, T.; Moriarty-Schieven, G. H.; Davis, G. R.; Butner, H. M.; Gear, W. K.; Dominik, C.; Walker, H. J. (2005). "Structure in the Epsilon Eridani Debris Disk". The Astrophysical Journal 619 (2): L187 – L190. Bibcode 2005ApJ...619L.187G. doi:10.1086/428348. 
9. ^ Thomas, Paul J. (2006). Comets and the origin and evolution of life. Advances in astrobiology and biogeophysics (2nd ed.). Springer. p. 104. ISBN 3540330860. http://books.google.com/books?id=lDbMELpF8EcC&pg=PA104. 
10. ^ ^{a b} Kenyon, Scott; Bromley, Benjamin (2007). "Stellar Flybys & Planetary Debris Disks". Smithsonian Astrophysical Observatory. http://www.cfa.harvard.edu/~kenyon/pf/dd/flyby.html. Retrieved 2007-07-23. 
11. ^ Raymond, Sean N.; et al (2011). "Debris disks as signposts of terrestrial planet formation". Astronomy & Astrophysics 530. arXiv:1104.0007. Bibcode 2011A&A...530A..62R. doi:10.1051/0004-6361/201116456. 
12. ^ "SIMBAD: Query by identifiers". Centre de Données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-fid. Retrieved 2007-07-17. 
13. ^ Greaves, J. S.; Wyatt, M. C.; Holland, W. S.; Dent, W. R. F. (2004). "The debris disc around tau Ceti: a massive analogue to the Kuiper Belt". Monthly Notices of the Royal Astronomical Society 351 (3): L54–L58. Bibcode 2004MNRAS.351L..54G. doi:10.1111/j.1365-2966.2004.07957.x. 
14. ^ ^{a b} Backman, D. E. (1996). "Dust in beta PIC / VEGA Main Sequence Systems". Bulletin of the American Astronomical Society 28: 1056. Bibcode 1996DPS....28.0122B. 
15. ^ Sanders, Robert (2007-01-08). "Dust around nearby star like powder snow". UC Berkeley News. http://www.berkeley.edu/news/media/releases/2007/01/08_dust.shtml. Retrieved 2007-01-11. 
16. ^ Lisse, C. M.; Beichman, C. A.; Bryden, G.; Wyatt, M. C. (1999). "On the Nature of the Dust in the Debris Disk around HD 69830". The Astrophysical Journal 658 (1): 584–592. arXiv:astro-ph/0611452. Bibcode 2007ApJ...658..584L. doi:10.1086/511001. 
17. ^ Beichman, C. A.; Tanner, A.; Bryden, G.; Stapelfeldt, K. R.; Werner, M. W.; Rieke, G. H.; Trilling, D. E.; Lawler, S.; Gautier, T. N. (2006). "IRS Spectra of Solar-Type Stars: A Search for Asteroid Belt Analogs". The Astrophysical Journal 639 (2): 1166–1176. arXiv:astro-ph/0601467. Bibcode 2006ApJ...639.1166B. doi:10.1086/499424. 
18. ^ Krist, John E.; et al. (October 2010). "HST and Spitzer Observations of the HD 207129 Debris Ring". The Astronomical Journal 140 (4): 1051–1061. Bibcode 2010AJ....140.1051K. doi:10.1088/0004-6256/140/4/1051. 
19. ^ ^{a b} Kalas, Paul; Graham, James R.; Clampin, Mark C.; Fitzgerald, Michael P. (2006). "First Scattered Light Images of Debris Disks around HD 53143 and HD 139664". The Astrophysical Journal 637 (1): L57–L60. arXiv:astro-ph/0601488. Bibcode 2006ApJ...637L..57K. doi:10.1086/500305. 
20. ^ Wyatt, M. C.; Greaves, J. S.; Dent, W. R. F.; Coulson, I. M. (2005). "Submillimeter Images of a Dusty Kuiper Belt around Corvi". The Astrophysical Journal 620 (1): 492–500. arXiv:astro-ph/0411061. Bibcode 2005ApJ...620..492W. doi:10.1086/426929. 
21. ^ Moerchen, M. M.; Telesco, C. M.; Packham, C.; Kehoe, T. J. J. (2006). "Mid-infrared resolution of a 3 AU-radius debris disk around Zeta Leporis". Astrophysical Journal Letters. arXiv:astro-ph/0612550. Bibcode 2007ApJ...655L.109M. doi:10.1086/511955. 
22. ^ Golimowski, D. et al. (2007). "Observations and Models of the Debris Disk around K Dwarf HD 92945" (PDF). University of California, Berkeley Astronomy Department. http://astro.berkeley.edu/~kalas/lyot2007/Presentations/Golimowski_David_poster.pdf. Retrieved 2007-07-17. 
23. ^ Williams, Jonathan P. et al. (2004). "Detection of cool dust around the G2V star HD 107146". Astrophysical Journal 604 (1): 414–419. arXiv:astro-ph/0311583. Bibcode 2004ApJ...604..414W. doi:10.1086/381721. 
24. ^ Marois, Christian; et al. (November 2008). "Direct Imaging of Multiple Planets Orbiting the Star HR 8799". Science Forthcoming (5906): 1348–52. Bibcode 2008Sci...322.1348M. doi:10.1126/science.1166585. PMID 19008415.  (Preprint at exoplanet.eu)
25. ^ Stark, C. et al. (2009). "51 Ophiuchus: A Possible Beta Pictoris Analog Measured with the Keck Interferometer Nuller". Astrophysical Journal 703 (2): 1188–1197. Bibcode 2009ApJ...703.1188S. doi:10.1088/0004-637X/703/2/1188. 
26. ^ Hines, Dean C. et al. (2006). "The Formation and Evolution of Planetary Systems (FEPS): Discovery of an Unusual Debris System Associated with HD 12039". The Astrophysical Journal 638 (2): 1070–1079. arXiv:astro-ph/0510294. Bibcode 2006ApJ...638.1070H. doi:10.1086/498929. 
27. ^ Furlan, Elise; Sargent; Calvet; Forrest; D'Alessio; Hartmann; Watson; Green et al. (2007-05-02). "HD 98800: A 10-Myr-Old Transition Disk". The Astrophysical Journal 664 (2): 1176–1184. arXiv:0705.0380. Bibcode 2007ApJ...664.1176F. doi:10.1086/519301. 
28. ^ Kalas, Paul; Fitzgerald, Michael P.; Graham, James R. (2007). "Discovery of Extreme Asymmetry in the Debris Disk Surrounding HD 15115". The Astrophysical Journal 661 (1): L85–L88. Bibcode 2007ApJ...661L..85K. doi:10.1086/518652. 
29. ^ Koerner, D. W.; Ressler, M. E.; Werner, M. W.; Backman, D. E. (1998). "Mid-Infrared Imaging of a Circumstellar Disk around HR 4796: Mapping the Debris of Planetary Formation". Astrophysical Journal Letters 503 (1): L83. arXiv:astro-ph/9806268. Bibcode 1998ApJ...503L..83K. doi:10.1086/311525. 
30. ^ ^{a b} Villard, Ray; Weinberger, Alycia; Smith, Brad (1999-01-08). "Hubble Views of Dust Disks and Rings Surrounding Young Stars Yield Clues". HubbleSite. http://hubblesite.org/newscenter/archive/releases/1999/03/text/. Retrieved 2007-06-17. 
31. ^ Meyer, M. R.; Backman, D. (2002-01-08). "Belt of Material Around Star May Be First Step in Terrestrial Planet Formation". University of Arizona, NASA. http://sse.jpl.nasa.gov/news/display.cfm?News_ID=2830. Retrieved 2007-07-17. 

External links

• McCabe, Caer (2007-05-30). "Catalog of Resolved Circumstellar Disks". NASA JPL. http://www.circumstellardisks.org/. Retrieved 2007-07-17.