Ubiquitous Brown Dwarfs: A Dark Matter Solution?

by Paul Gilster on April 22, 2009

Three brown dwarfs with masses that push up against the boundary between star and planet have been identified in IC 348, a star-forming region some 1000 light years from Earth in the direction of the constellation Perseus. The dwarfs do not appear to be gravitationally bound to a star although they are bound by the cluster, and they’re useful as we try to broaden our understanding of the mass distribution in newly formed stellar populations.

Andrew Burgess (Observatoire de Grenoble) has this to say about the find:

“There has been some controversy about identifying young, low mass brown dwarfs in this region. An object of a similar mass was discovered in 2002, but some groups have argued that it is an older, cooler brown dwarf in the foreground coinciding with the line of sight. The fact that we have detected three candidate low-mass dwarfs towards IC 348 supports the finding that these really are very young objects.”

ic348_arrow


Image
: IC 348, the star-forming region where the brown dwarfs were discovered. Credit: Adam Block and Tim Puckett.

Bear in mind that brown dwarfs cool with age. This news release indicates that current models show temperatures of between 600-700 degrees Celsius for the objects, extremely cool for newly formed brown dwarfs, with the implication of low mass. Again we push into areas of brown dwarf and sub-stellar object discovery that show how much work we have ahead as we catalog the local neighborhood.

So are brown dwarfs ubiquitous, occurring in sufficient numbers to account for an appreciable amount of the ‘dark matter’ in the galaxy? Studies are ongoing, but the three major ones that have already been completed indicate that the answer is no. The MACHO Project (Massive Astrophysical Compact Halo Object, a term for large astronomical bodies that can explain what seems to be dark matter in galactic haloes), along with the EROS and OGLE collaborations, all involved studies of the Small and Large Magellanic Clouds, satellite galaxies to our own Milky Way.

Using stars in the LMC and SMC as light sources, the teams observed the stars for several years and looked for the kind of lensing events that would indicate the presence of a dark object between the star and the observer. The MACHO and EROS teams announced the detection of three MACHOs as far back as September of 1993. That was after looking at 1.8 million stars for one year (MACHO) and 3 million stars for three years (EROS). By the end of the decade, the teams had a combined score of about twenty microlensing events.

Here’s a quote from Evalyn Gates’s new book Einstein’s Telescope: The Hunt for Dark Matter and Dark Energy in the Universe (W.W. Norton, 2009), a survey of where we stand on dark energy and dark matter studies with a focus on gravitational lensing:

The final paper of the MACHO collaboration, published in 2000, concluded that a Galactic halo consisting entirely of MACHOs was now ruled out, and estimated that about 20% of the Galactic halo was in the form of MACHOs. The EROS team preferred to present its results as an upper limit on the number of MACHOs in the halo, with no more than about 8% of the halo in MACHOs having masses of about one-tenth to one times the mass of the Sun. A combined analysis of the two experiments showed that, within the uncertainties of each experiment, they are consistent with each other and that less than 20% of the halo is in the form of MACHOs.

Gates goes on to say:

MACHOs, the least exotic candidates for dark matter, have now been effectively ruled out as the main component of the dark matter, leaving WIMPs to dominate the Galaxy…. Nevertheless, there seems to be evidence for some MACHOs in the Galactic halo, even if not enough to be interesting from a dark matter point of view.

WIMPs are Weakly Interacting Massive Particles, hypothetical particles that cannot be seen directly and do not interact strongly with atomic nuclei. That makes them far more exotic than MACHOs as a dark matter solution, but currently they seem to have taken the lead over the MACHO theory. Given the progress of our studies in these matters, though, it would be premature to call this investigation over, and further dark matter surprises seem likely.

James M. Essig April 22, 2009 at 16:04

Hi Folks;

Even thought the MACHOs may make up only about 20% of the galactic halo, that still implies a huge concentrated source of hydrogen for future galactic scale and super-galactic scale civilizations to harness.

Also, a cool temperature of only 400 degrees would make an excellent black body, no pun entended, emmitter in which to set up colonies for future human interstellar space fearing civilization. The light emmitted by such a star would be almost red and so with evolved eyes, either naturally or technologically, such brown dwarfs might make excellent luminaries to provide light for these colonies.

Adam April 22, 2009 at 17:31

Nice timing. There’s a news-bite from “New Scientist”…

http://www.newscientist.com/article/mg20227044.900-failed-stars-may-be-common-in-our-galaxy.html

…basically a brown dwarf microlensed a star towards the Galactic Bulge and it may indicate an enhanced number of the little blighters. The news-bite is very brief, but points to a paper…

http://arxiv.org/abs/0904.0249

The Extreme Microlensing Event OGLE-2007-BLG-224: Terrestrial Parallax Observation of a Thick-Disk Brown Dwarf
Authors: A. Gould , et.al. (65 authors)
(Submitted on 1 Apr 2009)

Abstract: Parallax is the most fundamental technique to measure distances to astronomical objects. Although terrestrial parallax was pioneered over 2000 years ago by Hipparchus (ca. 140 BCE) to measure the distance to the Moon, the baseline of the Earth is so small that terrestrial parallax can generally only be applied to objects in the Solar System. However, there exists a class of extreme gravitational microlensing events in which the effects of terrestrial parallax can be readily detected and so permit the measurement of the distance, mass, and transverse velocity of the lens. Here we report observations of the first such extreme microlensing event OGLE-2007-BLG-224, from which we infer that the lens is a brown dwarf of mass M=0.056 +- 0.004 Msun, with a distance of 525 +- 40 pc and a transverse velocity of 113 +- 21 km/s. The velocity places the lens in the thick disk, making this the lowest-mass thick-disk brown dwarf detected so far. Follow-up observations may allow one to observe the light from the brown dwarf itself, thus serving as an important constraint for evolutionary models of these objects and potentially opening a new window on sub-stellar objects. The low a priori probability of detecting a thick-disk brown dwarf in this event, when combined with additional evidence from other observations, suggests that old substellar objects may be more common than previously assumed.

…perhaps implying there’s something fishy making more brown dwarfs at low masses than previously thought.

philw1776 April 22, 2009 at 20:56

I’m not convinced. Without having the specific #s before me for BDs to explain Dark Matter the mass of BDs would have to exceed the mass of all stars, gas and dust by several tens of times. That means that there would have to be thousands of TIMES more BDs than we believe exist, not just several times or even 10x. I say NFW do BDs explain DM. Not that I have the answer. I’m starting to totally reassess my thinking on this…maybe there IS something wrong with our large scale theories of gravity after all.

Doowop April 23, 2009 at 8:53

First, I want the thank the Administrator for his kind words concerning my previous comment on this subject and how it inspired this post. You sure do know how to make a guy who knows little about astronomy feel very important and smart.

I do hope that BDs explain (at least in part) the DM and missing mass of the universe. Even a ratio of 100s of BDs per star would proably not be excessive, providing only a fraction of the missing DM. If there are 100s of BDs per star, interstellar exploration just got a lot easier. Instead of one massive voyage to a star (like the European voyages of discovery) we can spread slowly across the space between the stars (like the Polynesians in the south Pacific). Island hopping is a lot easier than ocean crossing.

Using terraforming and para-terraforming techinques developed for Mars and Venus (and maybe the Moon, Europa and other satellites) we could establish viable, self sifficient colonies at each stop on moons (planets?) orbiting warm BDs in their liquid water zones. Maybe Capt. Kirk and Darth Vader would not be impressed, but we could create mini space empires and federations using non-exotic propulsion techniques. We may also find that life based on visible-light spectrum photsynthesis is the rare exception and most life in the universe is infrared based.

IMHO, this would also be a cool idea for a Space Opera (books, TV series, movie franchise). Most “aliens” depicted in SF are just humans with bumpy foreheads anyways. But with some genetic engineering or tweaking of colonists we could create dozens of human derived new species suitable for colonizing BD worlds (at least as many as are members of Star Trek’s Federation or have seats in Star War’s Galactic Senate). Instead of “discovering new life and new civilizations”, the fictional star ship’s mission would be to “create” them. There would be no need for unscientific “science” to explain propulsion and other technologies. We could have a Space Opera that doesn’t break the laws of physics and rely on fantasy-science like warp drive or hyperspace.

Administrator April 23, 2009 at 13:24

Hey, they were excellent comments, Doowop, and so are these latest thoughts. A series set in a world of genetically adapted humans living on brown dwarf worlds would have my full attention! I assume you’ve read Karl Schroeder’s book Permanence re habitable brown dwarfs? Wonderful novel.

Administrator April 23, 2009 at 13:30

philw writes:

Not that I have the answer. I’m starting to totally reassess my thinking on this…maybe there IS something wrong with our large scale theories of gravity after all.

Could well be, although here again it gets tricky. You can adjust the gravitational model as per MOND (Modified Newtonian Dynamics) methods to work out the anomalous galactic rotations, but then you still have to re-invent dark matter to explain cluster lensing and other such effects. Evalyn Gates gets into a thorough look at this in her new book. It’s clear we’re a long way from the definitive answer.

keith bradshaw April 23, 2009 at 13:37

Hold on a bit Doowop ! Only a few days ago on this very site we had an article constraining the minimum distance to any unknown massive body to 100′s or 1000′s of AU. (At least I think so -it wasn’t clear from the abstract if the body had to be gravitationally bound to the sun or not.)

Also, the population of massive substellar objects must be constrained by the fact that the solar system is not regularly disrupted by close encounters with them.

Having said that, it’s clear there is at least a few scientists who believe BD’s to be at least as common if not more common than proper stars. This can be seen by the following link:

http://adsabs.harvard.edu/abs/2009AAS…21345907M

Doowop April 23, 2009 at 14:46

Keith,

IIRC 1 LY = about 64,000 AU. I also recall a nice 3d coordinate table for all the nearby stars within 70 LY of Sol in the back of my old copy of “The Starflight Handbook”. Further (again IIRC) by dividing the volume of a 70 LY sphere by the number of stars on the list you get an average volume of 8 cubic LY per star (2 LY ^ 3 on average) at least in our part of the galactic arm. Even at a minimum distance of 1000 AU (or about 6 “light*days”) between large stellar masses, this seems like enough elbow room for thousands of BDs per average around each star.

Unless of course I made a bone-headed math error.

Admin-guy,

I haven’t read Permanence but it looks like an interesting book and I’ll add it to my reading list. Any other BD based SF out there or is this too new of a concept?

Doowop April 23, 2009 at 14:50

Just out of curiosity, assuming that hundreds of BDs surround each star, what propulsion system would be appropriate for distances measured in light*days or light*weeks instead of light*years?

Doowop April 23, 2009 at 15:13

BTW what exactly do you call a body orbiting a BD?

Is it a planet? Moon? Planetoid? Object?

Adam April 23, 2009 at 22:39

Hi All

There are two “Dark Mass” problems, related but distinct. One is the flat rotation curves of the spiral Galaxies, the other is the cluster mass problem. The flat rotation curve problem is what is being discussed with respect to Brown Dwarfs, and it’s only a small multiple of the visible “Bright Mass” seen in the Galactic Disk. As you move away from the “Bright Mass” into Intergalactic space, the apparent mass as evidenced by gravitational lensing, cluster energetics and X-ray emissions from very hot gas, that mass goes up very quickly to large multiples of the “Bright Mass”.

Now we know some fraction of the Disk “Dark Mass” must be normally invisible gas, as it can be seen at other frequencies, but a significant fraction of it must be either “Dark Matter”, which doesn’t interact with regular light, or “Dark Objects” which are compact enough to not interfere with the usual passage of the light we can see. It can’t be opaque dust, because we’d notice the dimming of stars that’d cause – or rather what we can observe of the dust indicates there’s not enough of it. So it’s either “Dark Matter” – which might just be something simple like “Shadow Matter” or something really bizarre – or it’s “Dark Objects”, as the new observation might indicate.

Or it’s Shadow Matter Objects… Shadow Matter was first proposed in the 1960s to account for an implied symmetry in the weak force sensitive particles. Basically Shadow Matter is just like our normal matter but with its own kind of electromagnetic and colour forces, but sharing the weak and gravity forces in common with regular matter. If there’s enough it then it would form Shadow Stars, brown dwarfs, planets etc. Even Shadow Matter Life.

Could there be a Shadow Milky Way right alongside the regular Milky Way? Could the Sun have a Shadow Binary companion? Could there be Shadow planets in our Solar System? The answer might be ‘yes’ to all three.

Ronald April 24, 2009 at 5:28

@Doowop:
As mentioned in an earlier thread, if you want a good inventory of stars within 70 ly, see the Nstars database (http://nstars.nau.edu/nau_nstars/). And for just the nearest 100 stars, seen RECONS (http://www.recons.org/).

The average density of (bright not brown) stars in our part of the MW galaxy is about 0.002 per cubic ly.

Apart from the fact, as per this article, that BDs can most probably not explain most of the DM in a galaxy, I have my doubts about the prospects for planets orbiting them. Since planetary mass seems to be related to both stellar mass and metallicity, I wonder whether there is enough planetary building material around BDs.
See also my post in the previous thread about Gliese 581: only about 7% of exoplanets discovered sofar are near M dwarfs, despite their galactic dominance. I would not be surprised if that relative scarcity proceeds and increases toward the lower end (i.e. BDs).

keith bradshaw April 24, 2009 at 8:16

Doowop, the RECONS data indicate an average stellar separation locally (10 parsec radius) of about 7.3 light-years:

http://www.chara.gsu.edu/RECONS/census.posted.htm

On the NStars site, it says they expect to find 7500 objects within 25pc. The local density of stars is much less than you say, it’s more like 500 cubic LY per star, not 8.

Although I take your point about a light year being 64,000AU etc, I still think a population of hundreds of massive substellar objects per star is stretching things. I believe the various IR surveys would have found objects more than about 20Mj nearer than a few LY already, if they were there.

I would say an object orbiting a BD is a planet. Really, the very definition of a BD should include the formation mechanism, which is the same as a star, but on a smaller scale. It would have a disc of planet formation material around it just like a star when it formed, and this has been actually observed around at least one BD.

keith bradshaw April 24, 2009 at 8:34

Doowop, here is an interesting paper connected to WISE (see link below). The key thing from our point of view is Figure 3 on page 4. On there, you can see the expected numbers of BD’s within 10pc assuming different mass distribution functions. The upper estimate (alpha =-1.0) gives several hundred BD’s within 10pc, ie a similar number to the number of stars in the same volume. I have to say however, the RECONS site I linked to in my previous message gives alpha =-1.2, which would increase this estimate somewhat. Still, this can’t be reconciled with hundreds of BD’s per star.

http://arxiv.org/ftp/arxiv/papers/0902/0902.2604.pdf

Doowop April 24, 2009 at 10:19

Those are all interesting points and informative links, thank you gentlemen.

Numbers aside, we really should come up with a new name. “Brown dwarfs” sounds kind of ugly and uncool. How about “dark stars”, “nonstars” or “unstars”?

Way cooler names, IMHO.

Ronald April 24, 2009 at 11:23

Dim dwarfs?

(although color *is* a common denominator for star types)

keith bradshaw April 24, 2009 at 11:55

I think we are stuck with “brown dwarf”, it has become too ingrained to change it now. It’s unfortunate on other counts because they are expected to appear magenta or other colours rather than brown in many cases.

Unfortunately also, there seem to be two sorts of brown dwarfs possible, massive “planets”, above the deuterium-burning mass, formed around a proper star, or independently-formed “failed stars” in interstellar space. I feel the distinction is important, because the latter could have quite an extensive planetary system of its own, whereas the former would probably be limited to satellite systems similar to Jupiter and Saturn.

Adam April 26, 2009 at 0:30

Magenta Dwarfs. Closer to their actual colours.

Of course there’s the “merge two/three words together” option which is so popular in astronomy. Pulsar. Quasar. Collapsar.

So… Magentar

From now on that’s what I’m calling them… magentars.

Except for those damned “magnetars” to confuse them with *sigh*

keith April 27, 2009 at 7:40

Adam and others: an isolated cool brown dwarf in interstellar space won’t have a colour (except arguably, “black” -if you call black a colour). It would only be visible because it blocks out the stars behind itelf.

Possibly if we had true colour night-vision goggles we might see its colour.

Also there is the potential for lightening in the atmosphere, but probably not aurorae. Gas giants in the solar system have powerful aurorae going on, but out in interstellar space I guess that won’t happen.

So all in all, there wouldn’t be much for the unaided eye to see. Just a hole in the star field perhaps with a bit of lightening going on.

ljk April 27, 2009 at 9:21

April 26, 2009

Did Dark Matter Annihilate Our Early Universe?

Written by Ian O’Neill

A billion years after the big bang, hydrogen atoms were mysteriously torn apart into a soup of ions.

380,000 years after the Big Bang, the Universe cooled from being a hot soup of plasma, to a temperature where protons and electrons could combine to form atoms. This calm period of neutral hydrogen in universal history didn’t last for long however. The neutral hydrogen atoms were ripped apart once more, by a mechanism that would go on to reionize the entire Universe, a process that eventually ended a billion years after the Big Bang.

It is thought the first stars that formed prior to the reionisation epoch probably pumped out some fierce ultraviolet radiation, ionizing the neutral hydrogen, but a new (controversial) theory has been put forward. Did dark matter have a role to play in the reionisation the Universe?

As 85% of the Universe is composed of a type of matter we have yet to fully account for, it seems only natural that scientists would be looking into the possibility that dark matter had a role to play soon after the Big Bang. Although scientists are fairly confident that the reionisation period was driven by the emissions from the very first stars, there are some observational factors that could suggest dark matter annihilation might have had a role to play in the evolution of the Universe.

This is according to Dan Hooper and Alexander Belikov from Fermilab in Batavia, Illinois, in any case. In their theory recently published, the researchers examine the physics behind dark matter annihilation as the mechanism that drove the reionisation epoch.

Full article here:

http://www.universetoday.com/2009/04/26/did-dark-matter-annihilate-our-early-universe/

Tobias Holbrook May 1, 2009 at 12:42

Taking out my calculator, I find that a brown dwarf 1000AU away is less than 6ld (light days) away. If that’s the separation between them, then an interstellar empire isn’t that far fetched. I’d use antimatter triggered D/He3 fusion to power the ships, flying brachistone (this is assuming a mag sail can’t be used to decelerate). If we can get to 1/4 of c, then that’s a months journey. Empires can be held together.

However, they aren’t likely to be that close together. Even if they’re 1lm (light month) distant, however, we can still have an empire. I imagine empires/federations/republics centred on a main sequence star, with a ‘sea’ of brown dwarfs inbetween, used for relay and refueling. As well as being destinations in their own right.

ljk July 1, 2009 at 14:49

Identification of All Dark Matter as Black Holes

Authors: Paul H. Frampton

(Submitted on 22 May 2009 (v1), last revised 22 Jun 2009 (this version, v2))

Abstract: For the universe I use dimensionless entropy $S/k = \ln \Omega$ for which the most convenient unit is the googol ($10^{100}$) and identify all dark matter as black holes whereupon the present entropy is about a thousand googols.

While the energy of the universe has been established to be about 0.04 baryons, 0.24 dark matter and 0.72 dark energy, the cosmological entropy is almost entirely, about $(1 – 10^{-15})$, from black holes and only $10^{-15}$ from everything else.

This identification of all dark matter as black holes is natural in statistical mechanics. Cosmological history of dark matter is discussed.

Comments: History of baryons discussed

Subjects: High Energy Physics – Theory (hep-th); Cosmology and Extragalactic Astrophysics (astro-ph.CO); Galaxy Astrophysics (astro-ph.GA); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics – Phenomenology (hep-ph)

Cite as: arXiv:0905.3632v2 [hep-th]

Submission history

From: Paul Frampton [view email]

[v1] Fri, 22 May 2009 08:40:15 GMT (26kb)

[v2] Mon, 22 Jun 2009 18:25:36 GMT (27kb)

http://arxiv.org/abs/0905.3632

ljk July 6, 2009 at 2:54

Hot spots and a clumpy disk: Variability of brown dwarfs and stars in the young Sigma Ori cluster

Authors: Alexander Scholz (SUPA, University of St. Andrews), Xiaoying Xu (University of Arizona), Ray Jayawardhana (University of Toronto), Kenneth Wood (St. Andrews), Jochen Eisloeffel (TLS Tautenburg), Ciara Quinn (St. Andrews)

(Submitted on 2 Jul 2009)

Abstract: The properties of accretion disks around stars and brown dwarfs in the SOri cluster (age 3 Myr) are studied based on NIR time series photometry supported by MIR spectral energy distributions. We monitor ~30 young low-mass sources over 8 nights in the J- and K-band using the duPont telescope at Las Campanas.

We find three objects showing variability with J-band amplitudes >0.5 mag; five additional objects exhibit low-level variations. All three highly variable sources have been previously identified as highly variable; thus we establish the long-term nature of their flux changes. The lightcurves contain periodic components with timescales of ~0.5-8 days, but have additional irregular variations superimposed — the characteristic behaviour for classical T Tauri stars.

Based on the colour variability, we conclude that hot spots are the dominant cause of the variations in two objects, including one likely brown dwarf, with spot temperatures in the range of 6000-7000 K. For the third one (#2), a brown dwarf or very low mass star, inhomogenities at the inner edge of the disk are the likely origin of the variability.

Based on mid-infrared data from Spitzer, we confirm that the three highly variable sources are surrounded by circum-(sub)-stellar disks. They show typical SEDs for T Tauri-like objects. Using SED models we infer an enhanced scaleheight in the disk for the object #2, which favours the detection of disk inhomogenities in lightcurves and is thus consistent with the information from variability.

In the SOri cluster, about every fifth accreting low-mass object shows persistent high-level photometric variability. We demonstrate that estimates for fundamental parameters in such objects can be significantly improved by determining the extent and origin of the variations.

Comments: Accepted for publication in MNRAS. 16 pages, 8 figures, 1 appendix

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Cite as: arXiv:0907.0476v1 [astro-ph.SR]

Submission history

From: Alexander Scholz [view email]

[v1] Thu, 2 Jul 2009 20:18:09 GMT (183kb)

http://arxiv.org/abs/0907.0476

ljk August 7, 2009 at 14:48

Pulsation powered by deuterium burning in brown bwarfs and very-low-mass stars

Authors: Ann Marie Cody

(Submitted on 5 Aug 2009)

Abstract: Pulsation powered by deuterium burning in brown dwarfs and very low mass stars has been put forth (Palla & Baraffe 2005) as a novel probe of the interiors of these objects in the 1-15 Myr age range. Previous observations have hinted at variability on the expected timescales of a few hours, suggesting but not confirming that the phenomenon is at work in young brown dwarfs.

We have recently carried out a dedicated campaign to search for this putative class of pulsators among known low-mass members of five young star clusters. Our survey achieves sensitivity to periodic oscillations with photometric amplitudes down to several millimagnitudes.

We present the census of variability over timescales ranging from minutes to days and discuss the current prospects for pulsation as a tool in the study of young, objects near the substellar boundary. As a byproduct, this work provides new insights into the distribution of stellar rotation periods at young ages via the detection of variability due to cool surface spots.

Comments: 5 pages, 4 figures. To appear in AIP proceedings “Stellar Pulsation: Challenges for Theory and Observation”, Eds. J. Guzik and P. Bradley

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Cite as: arXiv:0908.0774v1 [astro-ph.SR]

Submission history

From: Ann Marie Cody [view email]

[v1] Wed, 5 Aug 2009 23:40:49 GMT (96kb)

http://arxiv.org/abs/0908.0774

ljk August 13, 2009 at 11:01

Dark Matter Phenomenology

Authors: Jonathan L. Feng

(Submitted on 10 Aug 2009)

Abstract: I review recent developments in the direct and indirect detection of dark matter and new candidates beyond the WIMP paradigm.

Comments: 6 pages, to appear in the Proceedings of the Tenth Conference on the Intersections of Particle and Nuclear Physics (CIPANP 2009), San Diego, California, 26-31 May 2009

Subjects: High Energy Physics – Phenomenology (hep-ph); Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

Report number: UCI-TR-2009-13

Cite as: arXiv:0908.1388v1 [hep-ph]

Submission history

From: Jonathan Feng [view email]

[v1] Mon, 10 Aug 2009 21:43:18 GMT (136kb)

http://arxiv.org/abs/0908.1388

ljk August 13, 2009 at 11:04

Dark Matter as a Possible New Energy Source for Future Rocket Technology

Authors: Jia Liu

(Submitted on 11 Aug 2009)

Abstract: Current rocket technology can not send the spaceship very far, because the amount of the chemical fuel it can take is limited. We try to use dark matter (DM) as fuel to solve this problem.

In this work, we give an example of DM engine using dark matter annihilation products as propulsion. The acceleration is proportional to the velocity, which makes the velocity increase exponentially with time in non-relativistic region.

The important points for the acceleration are how dense is the DM density and how large is the saturation region.

The parameters of the spaceship may also have great influence on the results. We show that the (sub)halos can accelerate the spaceship to velocity $ 10^{- 5} c \sim 10^{- 3} c$. Moreover, in case there is a central black hole in the halo, like the galactic center, the radius of the dense spike can be large enough to accelerate the spaceship close to the speed of light.

Comments: 7 pages, 6 figures

Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO); High Energy Physics – Phenomenology (hep-ph)

Cite as: arXiv:0908.1429v1 [astro-ph.CO]

Submission history

From: Jia Liu [view email]

[v1] Tue, 11 Aug 2009 01:58:10 GMT (502kb)

http://arxiv.org/abs/0908.1429

Tobias Holbrook September 19, 2009 at 10:56

Sort of like a Bussard Ramjet, but with much more plentiful fuel?

Charles Ivie December 23, 2009 at 20:09

Recent observations of M82 in the infrared reveal a large number of objects in the halo that had not been previously noticed. It is not yet clear if these exist in sufficient number to alter the dark matter models but further studies would seem to be advisable. The newly launched WISE spacecraft may prove to be a powerful tool in the search for low luminosity objects and could shed light (pun intended) on the dark matter question.

On the question of interstellar probes, I worked on a study about 30 years ago on an ion drive spacecraft powered by a fast spectrum reactor. (L. D. Jaffe and C. V. Ivie, Icarus, 39, 486-494 (1979) , It is exciting to realize that a growing number of scientists are taking the possibility of interstellar missions seriously.

Joseph Arellano August 25, 2012 at 23:21

I have no science background, therefore a nuisance. I believe, however, I found not only dark matter and dark energy but also many science questions.

Nothing springs from nothing; there always has to be raw material. Who has ever asked how did our universe, that started as a dot, reach its present size? And when the life span of that object is reached, it would release the elements it has collected. A fruit and so is a flower emit sweeter smell as it ripens until it rots. What become of mushrooms, mildews, fungus and the like for them to spring to life?

When that dot exploded to become the universe, as the small-small fragmentations spun they collected elements that made them what they are now. These elements are the raw material for them to increase in size. These elements are dark matter. Once their life span is reached they would seek the center of their origin. Seeking the center of the mass explains gravity. As they gravitate to form a single object that they once were, they release the elements they have gathered – the way a ageing fruit would emit its elements. The released elements become dark matter awaiting to be collected by the next fragmentations once the next explosion takes place.

Not only are dark matter abundant in outer space but also we are enveloped by it. It explains how mushrooms mushroom. Dark matter on earth could not be detected because present science gadgets has not the capability to detect their volume, which is not as large as those in outer space.

When atoms were smashed against each other, it resulted in countless particles. These are dark matter.

Dark matter are not visible because as elements they need other elements to form matter. Then only then could become visible and possess identity. Just like the atom that needs to co-mingle with other kinds of atoms to form an obect.

The mysterious force refer to as dark energy is the same force that keeps the atom oscillate on its own. This is because the law governing imperceptible atom is exactly the same law that governs the universe. Size is a matter of number.

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