by Paul Gilster | Sep 13, 2006 | Deep Sky Astronomy & Telescopes |
What are being described as the ‘deepest infrared and optical data ever taken’ provide a new picture of the early evolution of the universe. Researchers have observed hundreds of bright galaxies from the era around 900 million years after the Big Bang and compared this catalog with a deeper look 200 million years earlier in time. The result: Only one galaxy, using the strictest criteria, turned up in the earlier period, an indication of vast changes in those 200 million years.
The work comes from Rychard Bouwens and Garth Illingworth (University of California – Santa Cruz), who used the Hubble Space Telescope to look at early galaxy formation in dark patches of sky like the Hubble Ultra Deep Field and the Great Observatories Origins Deep Survey fields. The mechanism at work in this period of galactic evolution seems obvious. Says Illingworth:
“The bigger, more luminous galaxies just were not in place at 700 million years after the Big Bang. Yet 200 million years later there were many more of them, so there must have been a lot of merging of smaller galaxies during that time.”
This was an era only a few hundred million years after the formation of the first stars. At these distances, astronomers are unable to detect the infant galaxies that would have merged to form the galaxies under study, which are themselves much smaller than the Milky Way. But it is likely that we are looking at galaxy precursors in measurements of the cosmic background radiation from the Wilkinson Microwave Anisotropy Probe (WMAP), showing up as density fluctuations in an otherwise homogeneous universe around 400,000 years after the Big Bang.
Image: Images of a galaxy at redshift 7.4 (inside white box) in the Hubble Ultra Deep Field. This galaxy is seen just 700 million years after the Big Bang. The galaxy disappears at optical wavelengths (left), but is seen clearly in the infrared (right), as shown in the image boxes at the bottom. Credit: Rychard Bouwens, Daniel Magee/UC-Santa Cruz.
Centauri Dreams‘ take: The James Webb Space Telescope may provide the next breakthrough in early galaxy formation, but until then, consider how much we continue to depend on the cosmic microwave background to conduct such studies. Which is why Richard Lieu and team’s work, recently discussed in these pages, seems so jarring. The University of Alabama at Huntsville study found oddities in the CMB that raised the possibility of its not being in the background at all.
Bouwens and Illingworth’s work on infant galaxies, as do so many studies, dovetails naturally with an assumption of a non-local CMB, and it fits in so well with everything we know about the early universe that there must be other explanations for the Huntsville findings. But it will be fascinating to see how the Huntsville work can be explained in ways that preserve the CMB, and the untangling of that conundrum will surely offer another new key to understanding the universe’s earliest days.
For more on early galaxies, see the excellent First Galaxies site. The above work appears as Bouwens and Illingworth, “Rapid evolution of the most luminous galaxies during the first 900 million years,” Nature 443 (14 September, 2006), pp. 189-192 (abstract available online). In the same issue of Nature is equally provocative work by a Japanese team which has discovered a galaxy at 12.88 billion light years. That paper is Iye et al., “A galaxy at a redshift z = 6.96,” pp. 186-188 in the September 14 issue, with abstract available here.
by Paul Gilster | Sep 12, 2006 | Culture and Society |
Freeman Dyson among others has speculated about the physical changes that could occur as the human species spreads into the cosmos. How will evolution deal with a colony world in a distant star system, and how long will it take before serious differentiation begins to occur? For that matter, what about the crew aboard a multi-generational starship — will humans have adapted so thoroughly to a space-borne environment when they arrive that some opt to make their planetary excursion no more than a brief research stop before pushing on to yet other solar systems?
Or will they one day adapt to the vacuum itself?
Such questions are called to mind by recent work from Virginie Millien (McGill University), whose new paper in the open source journal PLoS Biology examines islands as test beds for evolution on Earth. It has long been assumed that isolation would create selective pressures unique to an island environment. A so-called ‘island rule’ has small animals evolving into outsized versions of their counterparts on the mainland, while larger animals tend to shrink. But although systematic evidence has been scarce, Millien’s work now confirms that island species do undergo accelerated evolutionary changes in small time frames.
How small? Anywhere from thousands of years down to decades, depending on the species. But the accelerated rate of evolution tends to slow down, until for intervals over 45,000 years the difference in evolutionary rates between mainland and island species becomes statistically insignificant. The big changes seem to involve the initial adaptation. Truly remote islands show the most interesting effects, but habitat destruction on the mainland can force equally quick changes. From the paper:
The commonly proposed mechanisms that govern evolution on islands — a founder event followed by slower evolution — can be compared to the mechanisms that operate after a drastic change in the environment on the mainland. However, the present data suggest that the peculiar ecological environment on islands — lack of predators, reduced interspecific competition, resource limitation — favours faster evolution, even over several thousands of years. Species surviving in fragmented landscapes are also confronted with a modified environment characterised by a reduced area and an increased isolation relative to their undisturbed habitat. These new environmental conditions parallel those seen in true island habitats, and one may suspect that morphological changes in response to fragmentation are similar to changes in island species.
Thus evolutionary rates vary with circumstances, as we would expect. Which brings to mind some of Dyson’s speculations about the evolution of future species adapted to space itself. But a shorter range outlook ponders what could happen even on places as relatively nearby as Mars once human colonies take hold there. Millien’s work offers the possibility that evolutionary changes to, for example, differing gravitational pulls will begin to produce serious species changes in fairly short time frames. Then throw in genetic engineering for some truly interesting effects. Here’s Dyson in Disturbing the Universe:
The Mongolian nomads developed a tough skin and a slit-shaped eye to withstand the cold winds of Asia. If some of our grandchildren are born with an even tougher skin and an even narrower eye, they may walk bare-faced in the winds of Mars. The question that will decide our destiny is not whether we shall expand into space. It is: shall we be one species or a million? A million species will not exhaust the ecological niches that are waiting the arrival of intelligence.
And a bit later:
When life invades a new habitat, she never moves with a single species. She comes with a variety of species, and as soon as she is estabished, her species spread and diversify still further. Our spread through the galaxy will follow her ancient pattern.
The above quotes are from my 1979 hardcover edition of Disturbing the Universe (New York: Harper and Row), both on p. 234. Millien’s paper is “Morphological Evolution Is Accelerated among Island Mammals, PLoS Biology Vol. 4 Issue 10 (September, 2006). And although I don’t have time to get into this today, the open access movement which PLoS Biology exemplifies is part of an ongoing revolution in science publishing that we’ll continue to examine in these pages.
by Paul Gilster | Sep 11, 2006 | Culture and Society |
The idea of interstellar flight forces long-term speculation. Barring unexpected breakthroughs, we are looking at mission times that, at best, are counted in the decades if not centuries. One of the purposes of Centauri Dreams is to encourage the kind of long-term thinking that plans and executes such missions. That such thinking — focused well beyond individual human lifetimes — is a worthy goal in and of itself should also be obvious, and it is actively championed in projects like the 10,000 year clock of the Long Now Foundation.
A partial spinoff from the Long Now called the Long Bets Foundation is increasingly active in providing a competitive arena for predictions about the future. It’s a fascinating concept, both a forum for discussion about long-range issues and a tool for philanthropic giving. People make predictions which, if challenged, become bets. Each prediction requires a $50 fee to the foundation, while a minimum of $200 is required to challenge a prediction. After a period of negotiations, the bet is finalized at whatever terms the two parties involved can agree on. Some bets go up well over the original $200. Winnings (with interest) are awarded to the winner’s preferred charity.
That assumes the winner is still alive at the time, which won’t always be the case. Paul Hawken, for example, offers a prediction that intelligent signals from beyond the Solar System will be received by the year 2050, while Kevin Kelly offers a 200 year prediction that downtown American cities in that era will look pretty much like they do today. I wish Kelly many years of good health, but he is unlikely to be here in 200 years; if his prediction is challenged and taken up as a bet, the foundation will choose a charity deemed closest to his original intentions as recipient for the money (assuming he’s the winner).
Some of these bets are going to inspire discussion for a long time, and of course that’s the idea. Thus Mitchell Kapor and Ray Kurzweil have squared off on the question: “By 2029 no computer – or “machine intelligence” – will have passed the Turing Test.” And here’s my favorite, pitting Danny Hillis against Nathan Myhrvold: “The universe will eventually stop expanding.” I don’t know how to figure the time frame on that one, but Hillis says yes and Myhrvold says no, and $2000 rides on the outcome. The accrued interest should light up the eyes of any surviving philanthropist.
Paging through the Long Bets site, you learn a good deal about what some very influential people are thinking. Michio Kaku and John Horgan are at odds over this one: “By 2020, no one will have won a Nobel Prize for work on superstring theory, membrane theory, or some other unified theory describing all the forces of nature.” And how about this: Freeman Dyson backs the notion that “The first discovery of extraterrestrial life will be someplace other than on a planet or on a satellite of a planet,” while Peter Spark says no.
The stakes in all these bets are placed in the Farsight Fund, managed by Capital Research and Management in Los Angeles. Take a look at this project to see how long-term thinking can be stimulated here and now through active discussion and philanthropic activity, and keep the Long Now Foundation in your list of active bookmarks as well. We live in a quick-turnaround, shortsighted era, a time desperately in need of an ability to focus beyond itself. That starts with individual decisions to think beyond a single lifetime for the good of the species, an ongoing effort that these two foundations continue to champion and one that Centauri Dreams applauds.
by Paul Gilster | Sep 9, 2006 | Exoplanetary Science |
Following hard on our discussion of HD 3651, a K-class dwarf whose brown dwarf companion was recently imaged, comes news that the Hubble Space Telescope has photographed something smaller still. CHRX 73 B orbits a low-mass red dwarf. Some would consider it a planet, others a brown dwarf; which camp you are in depends on what you use as a planetary marker. If it’s mass, then this object, 12 times the mass of Jupiter, would probably be considered a planet. But team leader Kevin Luhman (Pennsylvania State) has other ideas.
For if your marker is how the object formed, then a whole new set of criteria swim into view. Luhman argues that to be a planet, an object must have evolved from the gas and dust disk that circles a newly formed star. Whereas brown dwarfs are thought to form like any other star, from the collapse of huge clouds of hydrogen gas. They simply lack the mass to ignite hydrogen fusion in their cores.
And Luhman seems to be on firm ground in making this distinction:
“The object is so far away from its star that it is unlikely to have formed in a circumstellar disk. Disks around low-mass stars are about 5 to 10 billion miles in diameter. There isn’t enough material at that distance from the red dwarf to create a planet. Theoretical models show that giant planets like Jupiter form no more than about 3-billion miles from their stars.”
Image: This NASA Hubble Space Telescope image shows one of the smallest objects ever seen around a normal star. The brown dwarf candidate, called CHXR 73 B, is the bright spot at lower right. It orbits a red dwarf star, dubbed CHXR 73, which is a third less massive than the Sun. At 2 million years old, the star is very young when compared with our middle-aged 4.6-billion-year-old Sun. Credit: NASA, ESA, and K. Luhman (Penn State University).
Centauri Dreams‘ take: Brown dwarfs, we now know, are plentiful in the galaxy, and most do not orbit stars. Can brown dwarfs form planetary systems of their own? The Spitzer Space Telescope has detected several disks around brown dwarfs, but it’s impossible to tell whether CHRX 73 B has one or not — it’s too close to its primary to make the call. Disk or not, this find is a milestone in small object detection and reminds us that the boundaries between planet, brown dwarf and main sequence star are still very much in play.
by Paul Gilster | Sep 8, 2006 | Exoplanetary Science |
Small telescopes doing amazing things. That’s the theme of the day in exoplanet hunting, reinforced by the announcement of a new planet discovered by the Trans-Atlantic Exoplanet Survey (TrES). Small, automated equipment and off-the-shelf camera technology went into this work, which spotted the third transiting planet found with the kind of telescopes available to amateurs. “Hunting for planets with amateur equipment seemed crazy when we started the project,” says David Charbonneau, an astronomer at the Harvard-Smithsonian Center for Astrophysics, “but with this discovery the approach has become mainstream.”
Image: A computer-generated simulation of TrES-2 crossing (transiting) the disk of its host star. TrES-2 transits farther from the disk center than any other known transiting planet. The transit of TrES-2 causes a drop in the brightness of its home star of about one and a half percent. This slight dimming of the star’s light was noticed and measured by the TrES researchers, who used the parameters of the transit to determine the planet’s mass, size and other properties. Credit: Jeffrey Hall, Lowell Observatory.
Here’s how TrES works: A network of small telescopes are automated to make wide-field exposures on observing runs that typically last about two months. The data, consisting of observations of tens of thousands of stars, are then run through software that examines the light curve of each, looking for the telltale signs of a planetary transit across the star. That’s no small task given the number of false positives that are bound to arise from binary star systems.
But when the data have been combed through and a suitable candidate found, the 10-meter instruments at the Keck Observatory on Mauna Kea (Hawaii) go to work to confirm the discovery. TrES also includes telescopes at the Palomar Observatory, the Planet Search Survey Telescope at Lowell Observatory in Arizona, and the Stellar Astrophysics and Research on Exoplanets (STARE) telescope in the Canary Islands.
Transits are terrifically useful finds because when they occur around nearby stars, they provide uniquely accurate size and mass measurements. The new world, TrES-2, blocks about one and a half percent of the light of its star, some 500 light years away in Draco. It’s larger than Jupiter and passes in front of the primary every two and a half days. Usefully, TrES-2 is also in a part of the sky that the upcoming Kepler mission will examine, allowing astronomers to plan ahead for a thorough examination of the planetary system. Adds Charbonneau, “TrES-2 will likely become the best-studied planet outside the Solar system once Kepler flies.”
This work has been submitted to the Astrophysical Journal Letters, and though I don’t yet see a link to it at arXiv, you can download a PDF of O’Donovan et al., “TrES-2: The First Transiting Planet in the Kepler Field” here. Also helpful by way of background is Charbonneau et al., “When Extrasolar Planets Transit Their Parent Stars,” available online.
