by Paul Gilster | May 8, 2008 | Deep Sky Astronomy & Telescopes |
It’s hard enough to figure out what dark energy and dark matter are, a task that will occupy physicists for a long time to come. But even if we confine ourselves to ‘normal’ or ‘baryonic’ matter (accounting only for some four or five percent of the universe), we’re still left with a problem. Baryons are heavy subatomic particles like protons and neutrons that experience the strong nuclear force, and the problem is that even these relatively familiar particles are only partially accounted for.
So where is the missing baryonic matter? The answer may lie in a thin haze of hot, low-density gas that connects galactic clusters. Call it WHIM, for warm-hot intergalactic medium. Dutch and German scientists now think they have uncovered a filament of such gas that connects the clusters Abell 222 and Abell 223. The properties of the gas, visible primarily in the far ultraviolet and X-ray bands, fit with simulations in terms of density and temperature. The scientists used the XMM-Newton X-ray observatory to identify the hitherto unobserved filament.
Image: Composite optical and X-ray image of galaxy clusters Abell 222 and Abell 223. The cluster pair is connected by a filament permeated by hot X-ray emitting gas. The optical image was obtained by SuprimeCam at the Subaru telescope, the X-ray image showing the distribution of the diffuse hot gas (yellow to red) was obtained by XMM-Newton. Credits: ESA/ XMM-Newton/ EPIC/ ESO (J. Dietrich)/ SRON (N. Werner)/ MPE (A. Finoguenov).
Norbert Werner (SRON Netherlands Institute for Space Research), who led this work, thinks the team is seeing at least some of the missing baryonic matter. Says Werner, “The hot gas that we see in this bridge or filament is probably the hottest and densest part of the diffuse gas in the cosmic web…”
That last phrase deserves explanation. I’m working through the paper, which likens the structure of the universe to such a web-like structure, with galactic clusters, the largest objects in the universe, congregating at the web’s densest nodes. Let me quote the scientists on this:
According to the standard theory of structure formation, the spatial distribution of matter in the Universe evolved from small perturbations in the primordial density field into a complex structure of sheets and filaments with clusters of galaxies at the intersections of this filamentary structure. The filaments have been identified in optical surveys of galaxies…, but the dominant fraction of their baryons is probably in the form of a low density warm-hot gas emitting predominantly soft X-rays.
Sheets and filaments, with the things we see clustering in the web’s threads and knots. Thirty to forty percent of the baryonic matter in the universe ought to reside in filaments connecting galactic clusters, according to a variety of simulations, but this seems to be the first unambiguous detection (although other candidates have been put forward). And while the observed filament closely tracks at least one previous simulation, we still haven’t seen the largest part of the missing matter:
…according to the simulations… the dominant fraction of the WHIM resides in a lower temperature and density phase, the existence of which still remains to be proven observationally. The detection of the dominant fraction of the WHIM will only be possible with dedicated future instrumentation…
In other words, we’re going to need a more advanced space-based observatory to extend such difficult work, this particular filament being detectable largely because it is along the line of sight from Earth, thus concentrating its emission in a small region of sky. Understanding how matter is distributed in these structures will help us better piece together this web-like structure and the place of baryons within it.
The paper is Werner, et al., “Detection of hot gas in the filament connecting the clusters of galaxies Abell 222 and Abell 223,” Astronomy & Astrophysics Letters, Volume 482-3 (May, 2008), p. L29 (abstract).
by Paul Gilster | May 7, 2008 | Asteroid and Comet Deflection |
By Larry Klaes
Any good news from Arecibo is welcome, and Larry Klaes here delivers it. The observatory, threatened with closure despite its key role in the hunt for Earth-crossing asteroids, may have found at least temporary deliverance. Politics seems to have played a role, as Larry notes, but for once with results that benefit science rather than compromising it. Meanwhile, a new study of the Chixculub impact 65 million years ago tells us that a hail of carbon cenospheres — tiny carbon beads — may have fallen planet-wide following the strike. The more we learn about past impacts, the more we realize how important a role our planetary radars play in forestalling future catastrophe.
What exists on the island of Puerto Rico that is over 1,000 feet across, could hold ten billion bowls of cereal, pick up a cell phone call from the planet Venus, once sent a message to any potential inhabitants of a distant globular star cluster, discovered the first planets around another star, has been a “star” in several major motion pictures, has spent the last two years under the threat of losing its funding, and now may be saved on several political fronts, including one involving a New York senator who has been rather busy these days running for President?
The answer is the Arecibo Observatory, which has been managed by Cornell University since it began exploring the Universe in 1963. Home to the largest single radio telescope on Earth, Arecibo has made many major discoveries for astronomy. The facility has also been prominent in analyzing planetoids known as Near Earth Objects (NEOs) that could potentially impact our planet and threaten all life upon it.
Despite all these achievements, in 2006 the National Science Foundation (NSF) appointed a senior advisory panel to see where they could get money for new astronomical projects by cutting funds from current projects. Arecibo was one of the larger targets for cuts, with a proposed removal of $2.5 million over the next few years. It became clear that if Arecibo could not find the financial resources from elsewhere, the venerable observatory could close down in 2011. Not only would this be a major loss to astronomy but also a blow to the economy of Puerto Rico and its important contribution to the science education of the population.
On April 14, the governor of Puerto Rico and the director of the National Astronomy and Ionospheric Center (NAIC) signed a $2.3 million agreement between the semi-autonomous United States territory and the agency that Cornell manages Arecibo through for the NSF. The “Inspiration to Science” program will allow tens of thousands of Puerto Rican school children to visit Arecibo annually to see how the observatory scientists work and receive personal instruction from facility staff consonant with their academic curricula. To handle this influx of students, two new teaching scientists and an aide will be hired. The Puerto Rico Department of Education will provide for the resource needs of the students participating in this program.
Image: Arecibo’s observatory appears to have new life ahead, a plus not only for observational science but the search for dangerous near-Earth objects. Credit: Lee Bennett/ATPM.
“For more than forty years, the Arecibo Observatory has been part of Puerto Rico, an icon recognizably identified with the island worldwide,” said NAIC Director Robert Brown at the signing ceremony. “With the agreement signed today, the people of Puerto Rico become fully part of the Arecibo Observatory, cementing a new relationship that will also become a proud heritage of Puerto Rico.”
As the “Inspiration to Science” initiative was inaugurated, another effort to save the Arecibo facility outright was launched thanks to the efforts of New York Democratic senator Hillary Rodham Clinton, who filed a bill to make the NSF reinstate its funding for the observatory.
Some residents noted that though the action by Clinton is welcome, the fact that it is happening less than two months before Puerto Rico’s final Democratic primary elections on June 1 leaves them wondering just how altruistic Clinton’s motivations were.
“Arecibo has been in peril for a while now,” said Andros Lopez to the Orlando Sentinel, an attorney and a co-director of the local campaign to elect rival Democratic candidate Barak Obama. “That she, by chance, finds about it now is an example of the type of old politics that Obama wants to change. The timing is more than suspect.” Lopez did add that he was grateful nevertheless to see that Clinton “finally pays attention to an issue that pertains to us.”
Arecibo Director Robert Kerr was just grateful for the Clinton’s desire to help the observatory, whatever the ultimate motivation.
“I am quite convinced that the excellence of the Arecibo Observatory will prevail,” declared Kerr regarding Clinton’s actions of support.
Senator Clinton’s Senate office published a release about her support for Arecibo, noting that “Cornell University scientists have used the remarkable tools available at Arecibo Observatory to greatly expand our understanding of the Universe. I am proud to support the path-blazing accomplishments of these New Yorkers.”
Regarding the actual stands of the major presidential candidates when it comes to science and space science in particular, Popular Mechanics recently reported on the candidates’ public declarations for national space policy and the reality behind their statements and motivations, which can be read online here.
A recent CNN report quoted experts in the space and military fields expressing the strong hope that the candidates will go beyond their spoken platitudes and address space policy in earnest soon. Not only are there political considerations to contend with in keeping America’s space program at the forefront, but having a robust ability to understand and monitor the Universe with such instruments as the Arecibo radio telescope – one of humanity’s greatest tools for studying and ultimately preventing NEOs that could strike Earth from hitting – is vital both for the United States and the rest of the world.
by Paul Gilster | May 6, 2008 | Asteroid and Comet Deflection |
One of the world’s largest impact craters (see below) lies under Mexico’s Yucatan peninsula, evidently a major player in the demise of the dinosaurs. Chicxulub is 180 kilometers in diameter, the subject of continuing research by the man who identified it, Alan Hildebrand (University of Calgary). So you could say Hildebrand has an idea what massive impacts from asteroids can do to the Earth’s surface, having studied the environmental effects caused by this one and mapping the crater’s structure to identify mineral, oil and gas resources. That interest has led Hildebrand into an ongoing asteroid hunt, and explains his current plans to build and launch a space-based observatory designed to look for near-Earth objects.
The scientist currently uses use a retrofitted satellite tracking telescope in NEO work here on Earth. The instrument, based at the University of Calgary’s Rothney Astrophysical Observatory (some 75 kilometers southwest of the city) is an extensive re-build, a Cold War era instrument whose motors were replaced, its mount and optics modified and its electronics brought up to speed several years ago at the cost of $500,000. The telescope has been in asteroid-spotting use ever since.
Image: What we’re all hoping to avoid, an artist’s conception of a near-Earth object heating up as it encounters the upper atmosphere. Credit: Melinda Wenner/Wired Magazine.
Taking the asteroid search into space in the form of the Near Earth Object Surveillance Satellite (NEOSSat), an event that could occur within two years, would create the first space-based asteroid telescope, one to be used not only for identifying potential threats but also for helping us firm up our inventory of asteroids near enough to the Earth for manned missions. Nor is the suitcase-sized microsatellite a costly investment, totalling $10 million. Its position in space should allow the observatory to block sunlight to look for objects between the Earth and the Sun that are otherwise difficult to see.
Because some of these asteroids come close to matching Earth’s orbital speed, a robotic or manned asteroid mission becomes a distinct possibility. That would offer not only useful information about the early Solar System — such asteroids being remnants of same — but would also help us take the measure of the kind of objects we might one day need to push out of Earth-impacting trajectories. Would nukes work? Gravitational tugs? Sooner or later we’ll fly a NEO mission because we need to understand the nature of these asteroids as we assess the various strategies for dealing with them.
NEOSSat has the potential of cataloguing at least 50 percent of the one-kilometer or larger NEOs that orbit largely between Earth and the Sun, as New Scientist reports. Interestingly, the magazine cites Timothy Spahr (Harvard-Smithsonian Center for Astrophysics) as saying that an even better idea (though obviously far more expensive) would be to place a NEO-watching observatory in orbit around Venus, where the inventory of inner system objects could be even more definitively compiled.
Addendum: Although I had original identified Chixculub as the world’s largest impact crater, reader James Davis Nicoll quickly corrected me. Both Vredefort (300 km) and Sudbury (250 km) are larger.
by Paul Gilster | May 5, 2008 | Astrobiology and SETI |
Our recent look at panspermia concepts was largely devoted to the transmission of life via microbes or spores here in our own Solar System. The even richer question of how life might pass from star to star is far more problematic, but as a follow-up to that earlier story, I want to look at work that graduate student Jess Johnson did with Jonathan Langton and advisor Greg Laughlin at the University of California, Santa Cruz. Their work suggests that while life might readily survive an interstellar journey, it is unlikely to wander close enough to seed another system.
Ponder the era here on Earth known as the Late Heavy Bombardment (LHB). After the period of planetary accretion ended some 4.4 billion years ago, life apparently began. But 3.8 to 4 billion years ago, the LHB saw the planet again pummeled, causing debris to be ejected into space. Looking specifically at the mass that is ejected at 16.7 kilometers per second in the direction of the Earth’s motion (this is Solar System escape velocity), Johnson, Langton and Laughlin found that a substantial amount of rock (about 5 X 1021 grams) would have been blasted free of the Sun.
Remember, this is a period after life has started, so biological material could presumably be involved in any materials lifted into space. But what could survive the 20,000 g’s the ejecta would have experienced, and then cope with vacuum, radiation, cosmic ray strikes and ultimate re-entry and collision upon arrival? Bacillus subtilis is a common bacteria that needs no oxygen to survive, uses carbon and nitrogen as nutrients and forms spores when it lacks the nutrients to thrive. The dormancy period we’re talking about runs into the tens of millions of years, obviously long enough for an interstellar journey — even our glacially slow (by interstellar standards) Voyager spacecraft could make it to the Centauri stars in 75,000 years or so if they were pointed in that direction.
Here’s a striking fact: A viable sample of Bacillis has been found in the stomach of a mosquito encased in amber that has been dated at 25 million years old. Moreover, Bacillus passes all the other tests, able to survive impact pressures upon arrival, capable of enduring 33,800 g’s and, shielded by a sufficient outer encasement of rock, more than able to withstand the radiation hazards of the journey. In deriving the amount of ejected materials (the 5 X 1021 grams mentioned above), the Santa Cruz team chose only those fragments of rock greater than one metre in diameter to ensure the necessary shielding.
So everything looks promising for interstellar panspermia except the possibility that such life-bearing rocks may make their way to another stellar system. Producing calculations on the odds of capture, the trio found a result discouraging for interstellar panspermia theorists:
The results of our work found that, although there are microrganisms that are easily capable of surviving all of the challenges of interstellar travel, the probability of capture by another planetary system is vanishingly small. It should be noted that this in no way negates the possibilty of transport between worlds in our own system, a situation that seems quite possible.
A poster on this work (though without the later results) can be found here.
Related: An upcoming paper by William Napier and Janaki Wickramasinghe (Cardiff Centre for Astrobiology) in Monthly Notices of the Royal Astronomical Society discusses the Solar System’s movement through the plane of the galaxy, suggesting that the chances of comet collision go up every 35 to 40 million years. The potential for disaster on Earth is obvious, but the paper argues that such impacts help life to spread. Says Chandra Wickramasinghe, the Centre’s director, “This is a seminal paper which places the comet-life interaction on a firm basis, and shows a mechanism by which life can be dispersed on a galactic scale.” Wickramasinghe collaborated with Fred Hoyle in the 1981 book Evolution From Space. More in this news release.
by Paul Gilster | May 3, 2008 | Missions |
From the first anniversary edition of the Carnival of Space, I’ll send you this week to Brian Wang’s discussion of two propulsion concepts for the near future. VASIMR (variable specific impulse magnetoplasma rocket) is under active development at Franklin Chang Diaz’ Ad Astra Rocket Company, a site to monitor for developments in a technology that offers potential specific impulses from 1,000 to 30,000 seconds.
That’s a major upgrade compared to conventional rocket designs, and one that could conceivably get us to Mars in as little as 39 days. The Finnish solar electric sail concept, which we’ve also looked at here, may be well enough along for a flight test in 2010, assuming the budgetary gods are smiling. Our next step outward depends upon bumping up trip times to relatively nearby destinations like Mars and the asteroids, and these are two of the more promising concepts for making that a reality.
