# Debris Disk Around a Dead Star

Our Solar System in the distant future may look something like the Helix nebula today. That’s because in about five billion years, the Sun will have become a white dwarf, its inner planets swallowed up by its earlier expansion, its outer planets, asteroids and comets surviving in distant orbits and colliding with each other to form a ring of dusty debris. The Sun will undergo, in other words, a kind of rejuvenation, experiencing what scientists call ‘late bombardment’ in a system that has become dynamically young again.

Such a disk has now been found in the Helix nebula, some 700 light years away in Aquarius. It took the infrared tools of the Spitzer Space Telescope to sort out the glow of the dusty disk that circles the remnant white dwarf between 35 and 150 AU out. The assumption is that the disk is the result of smashups in the outer system, presumably involving objects like those in our Kuiper Belt or comets from an Oort-like cloud.

Image: Spitzer’s infrared view of the Helix nebula. Infrared light from the outer gaseous layers is represented in blues and greens. The white dwarf is visible as a tiny white dot in the center of the picture. The red color in the middle of the eye denotes the final layers of gas blown out when the star died. The brighter red circle in the very center is the glow of a dusty disk circling the white dwarf (the disk itself is too small to be resolved). Credit: NASA/JPL-Caltech/K. Su (Univ. of Arizona).

A dusty disk found last year around the white dwarf G29-38 had shown that objects like these could survive around dead stars, though the disk around G29-38 was much closer to its star. We obviously have much to learn about debris disks in such settings. And what exactly does happen when a Sol-like star becomes a red giant? Here’s a snippet from the paper on this work (references edited out; see the preprint):

It has been established that any planet closer than ~1 AU will be engulfed by an expanding red giant…, while planets outside ~5 AU from the Sun will survive post-main-sequence evolution…, and the orbits of surviving planets and most of the Kuiper Belt objects (KBOs) and Oort Cloud comets will expand adiabatically and remain bound to the solar system… The re-stabilized KBOs and Oort Cloud can later become the source of objects that go into the inner part of the system, either plunging into the white dwarf or breaking up due to tidal destruction, and they can populate the inner system with dust.

The newfound debris disk may be solving a different mystery as well. The Helix nebula’s white dwarf is known to be emitting highly energetic x-rays, leading some astronomers to believe it was accreting matter from a hidden companion star. But disk material falling onto the star and triggering the outbursts seems to be a more satisfactory answer. “The high-energy X-rays were an unsolved mystery, said You-Hua Chu (UIUC). “Now, we might have found an answer in the infrared.”

The paper on this work is Su et al., “A Debris Disk around the Central Star of the Helix Nebula?,” which will appear in Astrophysical Journal Letters. The preprint is already available online.

Comments on this entry are closed.

• djlactin February 14, 2007, 1:19

beautiful image! what’s the scale?

• Administrator February 14, 2007, 8:04

The image scale: 31.5 x 23.7 arcmin, as per Spitzer info.

• ljk February 14, 2007, 11:18

Astrophysics, abstract
astro-ph/0701474

From: Carl H. Gibson [view email]

Date (v1): Tue, 16 Jan 2007 17:50:50 GMT (892kb)

Date (revised v2): Tue, 13 Feb 2007 13:25:36 GMT (825kb)

Interpretation of the Helix Planetary Nebula using Hydro-Gravitational-Dynamics: Planets and Dark Energy

Authors: Carl H. Gibson (UCSD), Rudolph E. Schild (Harvard)

Comments: 46 pages 11 figures, see this http URL for further information and higher resolution figures

Hubble Space Telescope (HST/ACS) images of the Helix Planetary Nebula (NGC 7293) are interpreted using the hydro-gravitational-dynamics theory (HGD) of Gibson 1996-2006. HGD predicts that baryonic-dark-matter (BDM) dominates the mass of galaxies (Schild 1996) as Jovian (promordial-fog-particle, PFP) Planets (JPPs) in proto-globular-star-cluster (PGC) clumps within galaxy halo diameters surrounding its stars. From HGD, supernova Ia (SNe Ia) events normally occur in planetary nebulae (PNe) within PGCs where binary clustering cascades of merging planets produce central binary star systems. As central stars of PNe, binaries exchange mass and accrete JPPs to grow white-dwarfs to $1.44 M_{\sun}$ instability within ionized (Oort cloud) cavities bounded by evaporating JPPs. SNe Ia events are thus intermittently obscured by radiation-inflated JPP atmospheres producing systematic SNe Ia distance errors, so the otherwise mysterious “dark energy” concept is unnecessary. HST/ACS and WFPC2 Helix images show $>7000$ cometary globules, here interpreted as gas-dust cocoons of JPPs evaporated by beamed radiation from its white-dwarf plus companion central binary star system. Mass for growing the stars, the PNe, and possibly a SNe Ia event, is accreted gravitationally from ambient BDM JPPs. Measured JPP masses $\approx 3 \times 10^{25}$ kg with spacing $\approx 10^{14}$ m support the HGD prediction that the density $\rho$ of galaxy star forming regions fossilize the density $\rho_{0} \approx (3-1) \times 10^{-17}$ kg m$^{-3}$ existing at 30,000 years in the plasma-epoch, when proto-superclusters fragmented in the expanding universe giving the first gravitational structures.

http://arxiv.org/abs/astro-ph/0701474

• ljk March 16, 2007, 9:39

Astrophysics, abstract
astro-ph/0703383

From: Amaya Moro-Martin [view email]

Date: Thu, 15 Mar 2007 04:07:54 GMT (694kb)

Extra-Solar Kuiper Belt Dust Disks

Authors: Amaya Moro-Martin, Mark C. Wyatt, Renu Malhotra, David E. Trilling

Comments: 18 pages, 5 figures. Chapter from the book “Kuiper Belt”, edited by A. Barucci, H. Boehnhardt, D. Cruikshank and A. Morbidelli. Forthcoming

The dust disks observed around mature stars are evidence that plantesimals are present in these systems on spatial scales that are similar to that of the asteroids and the KBOs in the Solar System. These dust disks (a.k.a. “debris disks”) present a wide range of sizes, morphologies and properties. It is inferred that their dust mass declines with time as the dust-producing planetesimals get depleted, and that this decline can be punctuated by large spikes that are produced as a result of individual collisional events. The lack of solid state features indicate that, generally, the dust in these disks have sizes larger than approximately 10 microns, but exceptionally, strong silicate features in some disks suggest the presence of large quantities of small grains, thought to be the result of recent collisions. Spatially resolved observations of debris disks show a diversity of structural features, such as inner cavities, warps, offsets, brightness asymmetries, spirals, rings and clumps. There is growing evidence that, in some cases, these structures are the result of the dynamical perturbations of a massive planet. Our Solar System also harbors a debris disk and some of its properties resemble those of extra-solar debris disks. From the cratering record, we can infer that its dust mass has decayed with time, and that there was at least one major “spike” in the past during the Late Heavy Bombardment. This offers a unique opportunity to use extra-solar debris disks to shed some light in how the Solar System might have looked in the past. Similarly, our knowledge of the Solar System is influencing our understanding of the types of processes which might be at play in the extra-solar debris disks.

http://arxiv.org/abs/astro-ph/0703383

• ljk May 9, 2007, 21:49

Planetary embryos and planetesimals residing in thin debris disks

Authors: Alice C. Quillen (Rochester), Alessandro Morbidelli (Nice), Alex Moore (Rochester)

(Submitted on 9 May 2007)

Abstract: We consider constraints on the planetesimal population residing in the disks of AU Microscopii, Beta Pictoris and Fomalhaut taking into account their observed thicknesses and normal disk opacities. We estimate that bodies of radius 5, 180 and 70 km are responsible for initiating the collisional cascade accounting for the dust production for AU-Mic, Beta-Pic and Fomalhaut’s disks, respectively, at break radii from the star where their surface brightness profiles change slope. Larger bodies, of radius 1000km and with surface density of order 0.01 g/cm^2, are required to explain the thickness of these disks assuming that they are heated by gravitational stirring. A comparison between the densities of the two sizes suggests the size distribution in the largest bodies is flatter than that observed in the Kuiper belt. AU Mic’s disk requires the shallowest size distribution for bodies with radius greater than 10km suggesting that the disk contains planetary embryos experiencing a stage of runaway growth.

submitted to MNRAS

Subjects:

Astrophysics (astro-ph)

Cite as:

arXiv:0705.1325v1 [astro-ph]

Submission history

From: Alice C. Quillen [view email]

[v1] Wed, 9 May 2007 16:50:17 GMT (21kb)

http://arxiv.org/abs/0705.1325

• ljk July 10, 2007, 12:18

Dynamics of Exozodiacal Clouds

Authors: M. Kuchner, C. Stark, O. Absil, J.-C. Augereau, P. Thebault

(Submitted on 9 Jul 2007)

Abstract: The inner Solar System contains a cloud of small (1-100 micron) dust grains created when small bodies-asteroids, comets, and Kuiper belt objects-collide and outgas. This dust cloud, the zodiacal cloud probably has extrasolar analogs, exozodiacal clouds. Exozodiacal clouds are related to debris disks, clouds of rocks and dust orbiting main sequence stars thought to represent the debris left over from planet formation. Some debris disks appear to contain distinct inner clouds that could be considered massive exozodiacal clouds (e.g. Koerner et al. 1998, Absil et al. 2006).

This white paper addresses the need for future theoretical work on the dynamics of exozodiacal clouds. This theoretical work should help us discover new planets and understand exozodiacal clouds as astrophysical noise. So far, observations of nearby stars have not provided good constraints on the structures of exozodiacal clouds. But future observations probably will demand a better theoretical understanding of these systems.

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0707.1280v1 [astro-ph]

Submission history

From: Philippe Thebault [view email]

[v1] Mon, 9 Jul 2007 15:13:48 GMT (1837kb)

http://arxiv.org/abs/0707.1280

• ljk August 2, 2007, 15:48

The Chemical Composition of an Extrasolar Minor Planet

Authors: B. Zuckerman (1), D. Koester (2), C. Melis (1), B. Hansen (1), M. Jura (1) ((1) UCLA, (2) University of Kiel)

(Submitted on 1 Aug 2007)

Abstract: We report the relative abundances of 17 elements in the atmosphere of the white dwarf star GD 362, material that, very probably, was contained previously in a large asteroid or asteroids with composition similar to the Earth/Moon system. The asteroid may have once been part of a larger parent body not unlike one of the terrestrial planets of our solar system.

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0708.0198v1 [astro-ph]

Submission history

From: Michael Jura [view email]

[v1] Wed, 1 Aug 2007 17:02:53 GMT (44kb)

http://arxiv.org/abs/0708.0198

• ljk August 2, 2007, 15:51

EF Cha: Warm Dust Orbiting a Nearby 10 Myr Old Star

Authors: Joseph H. Rhee, Inseok Song, B. Zuckerman

(Submitted on 8 Jun 2007 (v1), last revised 31 Jul 2007 (this version, v2))

Abstract: Most Vega-like stars have far-infrared excess (60 micron or longward in IRAS, ISO, or Spitzer MIPS bands) and contain cold dust (less than ~150K) analogous to the Sun’s Kuiper-Belt region. However, dust in a region more akin to our asteroid belt and thus relevant to the terrestrial planet building process is warm and produces excess emission in mid-infrared wavelengths. By cross-correlating Hipparcos dwarfs with the MSX catalog, we found that EF Cha, a member of the recently identified, ~10 Myr old, “Cha-Near” Moving Group, possesses prominent mid-infrared excess. N-band spectroscopy reveals a strong emission feature characterized by a mixture of small, warm, amorphous and possibly crystalline silicate grains. Survival time of warm dust grains around this A9 star is less than ~ 1E5 yrs, much less than the age of the star. Thus, grains in this extra-solar terrestrial planetary zone must be of “second generation” and not a remnant of primodial dust and are suggestive of substantial planet formation activity. Such second generation warm excess occurs around ~ 13% of the early-type stars in nearby young stellar associations.

Comments: New Spitzer MIPS data added; 14 pages, 1 figure, ApJ in press

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0706.1265v2 [astro-ph]

Submission history

From: Joseph Rhee [view email]

[v1] Fri, 8 Jun 2007 22:05:08 GMT (24kb)

[v2] Tue, 31 Jul 2007 23:05:31 GMT (25kb)

http://arxiv.org/abs/0706.1265

• ljk February 28, 2008, 7:19

Pollution of single white dwarfs by accretion of many small asteroids

Authors: M. Jura (UCLA)

(Submitted on 27 Feb 2008)

Abstract: Extrapolating from the solar system’s asteroid belt, we propose that externally-contaminated white dwarfs without an infrared excess may be experiencing continuous accretion of gas-phase material that ultimately is derived from the tidal destruction of multiple small asteroids. If this scenario is correct, then observations of metal-polluted white dwarfs may lead to determining the bulk elemental compositions of ensembles of extrasolar minor planets.

Comments: AJ, in press, 19 pages, 4 figures

Subjects: Astrophysics (astro-ph)

Cite as: arXiv:0802.4075v1 [astro-ph]

Submission history

From: Michael Jura [view email]

[v1] Wed, 27 Feb 2008 19:46:55 GMT (28kb)

http://arxiv.org/abs/0802.4075

• ljk March 10, 2008, 22:32

Astronomers at the University of Rochester have announced that low-mass stars, and maybe even super-Jupiter-sized planets might actually be responsible for the beautiful puffy nebulae. Their research appears in the latest editions of the Astrophysical Journal Letters and Monthly Notices of the Royal Astronomical Society.