Archive for the ‘Stars in their eyes’ Category

Why SETI will have missed any cost conscious ET civilizations

Friday, October 24th, 2008

meti-beacon.jpg

If we want to contact any of those other civilizations out there, we’ll need a beacon to send messages with. But what to build?

Gregory Benford at the University of California Irvine and family (?) have done a cost/benefit analysis on the types of microwave generators out there that can produce the 10^17 W necessary to reach a significant proportion of the galactic habitable zone.

There are various ways that the cost can be optimised and the Benfords summarise them like this:

“Thrifty beacon systems would be large and costly, have narrow searchlight beams and short dwell times when the Beacon would be seen by an alien observer at target areas in the sky. They may revisit an area infrequently and will likely transmit at high microwave frequencies, ~10 GHz. The natural corridor to broadcast is along the galactic spiral’s radius or along the spiral galactic arm we are in.”

This has implications for the search for ET civilisations (as opposed sending messages for them). If ET civilisations are as cost conscious as we are,  then they may well have built beacons in this way.
And if so, say the Benfords, nearly all SETI searches to date would have missed them.

Ref:

arxiv.org/abs/0810.3964: Cost Optimized Interstellar Beacons: METI

arxiv.org/abs/0810.3966: Cost Optimized Interstellar Beacons: SETI

How alien Earths will reveal their secrets

Friday, October 3rd, 2008

The European Space Agency has set itself an ambitious goal: to recognise the biomarkers on Earth-like planets orbiting other stars.

The first step in such an endeavour is work out to look for, which the goal that Lisa Kaltenegger at the Harvard-Smithsonian Center for Astrophysics in Cambridge  and Franck Selsis at the Laboratoire d’Astrophysique de Bordeaux in France have set themselves.

“The spectrum of the planet can contain signatures of atmospheric species that are important for habitability, like CO2 and H2O, or resulting from biological activity (O3, CH4, and N2O),” they say.  “The presence or absence of these spectral features will indicate similarities or differences with the atmospheres of terrestrial planets.”

But  just how similar is a question of some controversy. In one of the most fascinating papers of all time, Carl Sagan and friends analyzed a spectrum of the Earth taken by the Galileo probe, searching for signatures of life. They concluded that the large amount of O2 and the simultaneous presence of CH4 traces are strongly suggestive of biology.

But a more detailed study of this parameter space is necessary and not just from a theoretical point of view, conclude Kaltenegger and Selsis.

And time is short. With over 300 giant exoplanets already detected it is only a matter of time, maybe only months, before astrobiologists will have their first alien test case to analyse.

Ref: arxiv.org/abs/0809.4042: Atmospheric Modeling: Setting Biomarkers in Context

Nanodiamonds lead to sharper images

Friday, September 19th, 2008

nanodiamond-imaging.jpg

Zap a diamond nanoparticle with laser light and it will fluoresce, emitting single photons if it is small enough.  That makes nanodiamonds extremely useful, say Aurélien Cuche at the Université Joseph Fourier in Grenoble and pals.

For a start, nanodiamonds are easily absorbed by cells, which allows them and the processes inside them to be tracked with ease.

But Cuche and co have found a more exciting use: they have attached a nanodiamond the tip of a scanning near field microscope to provide single photon illumination when needed. And this dramatically improves the resolution of these devices, says the team.

Which means that nanodiamonds, cough, are a microscopist’s best friend.

Ref: arxiv.org/abs/0809.2026: Diamond Nanoparticles as Photoluminescent Nanoprobes for Biology and Near-Field Optics

How supermassive black holes help galaxies evolve

Friday, September 12th, 2008

black-hole-nasa.jpg

It’s easy to imagine that our understanding of the way galaxies form and evolve is more or less complete. After all, we’ve been fitting missing pieces into the jigsaw at an alarming rate in recent years with all this data from WMAP etc about the structure of the early universe, a better understanding of the distribution of dark matter and the vast computer simulations that show how galaxies should appear out of this maelstrom.

But there are one or two hairs in this astrophysical ointment. For example, our models of galaxy formation indicate that certain types of galaxies should become surrounded by huge clouds of gas in which stars ought to be forming. But observations show that there are far fewer of these types of galaxies than the models predict.

Today, Timothy Heckman of Johns Hopkins University in Baltimore discusses the idea that supermassive black holes at the center of these galaxies might explain the difference. The thinking is that black holes generate and spread enough energy to the outer reaches of the galaxy to regulate star formation in a way that fits with observations. We’ve certainly seen good evidence of supermassive black holes in various galaxies, including our own.

But what makes Heckman’s discussion highly provocative is the suggestions that a symbiotic relationship exists between galaxies and supermassive black holes, that they need each other to form. So supermassive black holes are as important in galactic evolution as gas, dust and gravity. What an idea!

What that means is that far from being a done deal, galaxy formation is set to become one of the hottest topics in astronomy as data from the next generation of space telescopes comes flooding in.

PS: Heckman has a great name for the study of gas-star-black hole cosmic ecosystems. He calls it gastrophysics. Like it!

Ref: arxiv.org/abs/0809.1101: The Co-Evolution of Galaxies and Black Holes: Current Status and Future Prospects

The ultimate black hole size limit

Tuesday, August 26th, 2008

ultramassive-black-holes.jpg

We have a pretty good idea that a supermassive black hole is sitting at the center of our galaxy. By supermassive, astronomers mean about 6 millions times as massive as our sun.

That’s pretty big by any standards but how big can black holes get Is there any limit to how big these monsters can become?

According to Priyamvada Natarajan at Yale University and a pal, the answer is yes.  Black holes, they say, cannot be bigger than 10^10 times the mass of the sun. (Or at least, are very unlikely to be bigger than that).

They arrive at this figure by calculating  the rate at which a black hole can swallow stuff and how much it could have gorged on since the universe was born, which seem like reasonable limits.

They call these beasts ultramassive black holes and reckon that there should be around 7×10^−7 of them per cubic megaparsec in the nearby universe. That’s not many. Our bast chance of finding one should be to look in the bright, central cluster galaxies in the local universe.

Better start scanning.

Re: arxiv.org/abs/0808.2813: Is there an upper limit to black hole masses?

How to find another Earth

Friday, August 22nd, 2008

 exoplanet.jpg

“We stand on a great divide in the detection and study of exoplanets,” says the Exoplanet Task Force on the arXiv today in describing their plan for finding another Earth orbiting another star.

On one side of this divide are the hundreds of known massive exoplanets, they say. And on the other” lies the possibility, as yet unrealized, of detecting and characterizing a true Earth analog–an “Earth-like” planet”.

And guess what, the Exoplanet Task Force knows how to bridge this divide.”

Their idea is to keep looking, using better telescopes. And when you find one, build a better telescope to look even harder.

It’s a strategy that’s guaranteed to succeed, provided you’re wearing a mask and a cape and call yourself the Exoplanet Task Force. Let’s face it, there’s nothing you can’t do while wearing your underpants on the outside.

Good luck fellas. We’re all behind ya.

Ref:  arxiv.org/abs/0808.2754: Worlds Beyond: A Strategy for the Detection and Characterization of Exoplanets

The black hole at the center of our galaxy

Thursday, August 21st, 2008

supermassive-black-hole.jpg

Is there a supermassive black hole at the center our galaxy, asks Mark Reid from the Harvard Smithsonian Center for Astrophysics in Cambridge.

There sure is and Reid gives a good account of the evidence to prove it.

How can astronomers be so sure?  The first evidence began to emerge in the 1950s when the first radio telescopes spotted a mysterious source of radio waves from the center of the Milky Way in the constellation of Sagittarius. This source was given the name Sagittarius A.

Better observations in the 1970s led to estimations that this source was small, less than the size of our solar system.

Towards the end of the 70s other evidence emerged. The movement of gas clouds near Sagittarius A indicated they it must circling a a compact mass several million times greater than the Sun. Then various stars were observed circling this mass, the most recent being a star called S2 which orbits Sagittarius A every 15.8 years. This implies that Sagittarius A is a point mass some 6 million times the sun’s mass

Then astronomers proved that the radio source and the gravitational  mass were centred at the same point. Other evidence of a weak infrared source at the same point also turned up.

And the clincher was that Sagittarius A is motionless relative to the rest of the Milky Way. In other words, the entire galaxy revolves around this object.

That kind of evidence is overwhelming. It’s hard to think of anything with such a dim optical signature that could create such a high mass density (although there are some possibilities, the most obvious being a cluster of dark stars).

Nevertheless, most astronomers are convinced we’ve got a super massive black hole on our doorstep and it’ll take some spectacular contradictory evidence to change their minds.

Ref:   arxiv.org/abs/0808.2624: Is There a Supermassive Black Hole at the Center our Galaxy

Solar systems like ours likely to be rarer than we thought

Wednesday, August 13th, 2008

planet-formation.jpg

Astronomers, to their obvious delight, have discovered some 250 planetary systems beyond our own, many of them with curious properties. In particular, the discovery of several “hot Jupiters” gas giants that orbit close to their parent stars, challenges our theories of planet formation.The thinking is that gas giants can only form far away from stars because gas and dust simply gets blown away from the inner regions.

Now Edward Thommes from the University of Guelph in Canada and pals think they know what must be happening. One idea is that gas giants migrate after they have formed. By performing a detailed numerical simulation of planet formation and repeating it many times using different starting conditions, Thommes and co say this looks a likely scenario. In fact, their data indicates that gas giant migration must be a common occurence.

But the data also has implications for us. A migrating gas giant sweeps away all in its path and that means that solar systems like ours are likely to be rare.

As Thommes and friends put it: “All of this leads us to predict that within the diverse ensemble of planetary systems, ones resembling our own are the exception rather than the rule.”

Shame!

Ref: arxiv.org/abs/0808.1439: Gas Disks to Gas Giants: Simulating the Birth of Planetary Systems

The weather on HD 189733b

Tuesday, July 15th, 2008

HD 189733B

Our old friend HD 189733b is in the news again this week. As a Jupiter-sized gaseous planet orbiting a yellow dwarf in the constellation of Vulpecula, HD 189733b has become one of the best studied exoplanets.

The reason is that it’s relatively big  and close to its sun, which shines through the atmosphere as the planet transits.

This phenomenon has allowed astronomers to measure many properties of HD 189733b’s atmosphere. For example, they have found that this ball of gas is rich in water and methane and that to our eyes the planet would appear a rich dark blue, a bit like Uranus.

Last year, the Spitzer Space Telescope produced a heat map of the planet showing global temperature differences. Unsurprisingly, HD 189733b is warmer at the equator than at the poles.

Astronomers also think the atmosphere is filled with particles of the condensates of iron, silicates and aluminium oxide. And today, Sujan Sengupta from the Indian Institute of Astrophysics in Bangalore, India, adds another nugget of information. It seems that these particles must be distributed in a thin layer of cloud in the upper atmosphere.

So if you’re wondering what the weather is like on HD 189733b, the answer is cloudy.

What’s emerging is the most amazing picture of a planet orbiting another sun, something that only a few years ago would have been deemed impossible.

To put this in perspective, our understanding and knowledge of HD 189733b is comparable to, and in some ways better than, our pre-Voyager knowledge of Neptune and Uranus in the 1970s.

That’s truly astounding. There can’t be many more persuasive examples of the fact that we’re currently living through a golden age of astronomy.

Ref: arxiv.org/abs/0807.1794: Cloudy Atmosphere of the Extra-solar Planet HD189733b : A Possible Explanation of the Detected B-band Polarization

Why red dwarfs could reveal first Earth-like planets

Thursday, July 10th, 2008

Earth-like planet

Red dwarfs are relatively common, cool stars that are less than half the size of the Sun. Because of their size, it should be easy to spot orbiting planets as they pass in front of the stars. For instance, a planet twice the size of Earth, orbiting in a star’s habitable zone at a distance of up to 8 AU, should reduce the luminosity of its host by up to 5 per cent as it transits.  That’s well within reach of many terrestrial scopes.

Which is why a group at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, have begun a systematic survey of the 2000 or so red dwarfs nearby.

The plan is to use 8 different 4o cm robotic scopes  to search the entire ensemble of red dwarfs for signs of habitable planets. Any found will then become among the most heavily studied objects in the cosmos

So although a number of space-based telescopes will be launched in the coming years to look for Earth-like planets around other stars, there’s a good chance the first discovery will be made a lot more cheaply using ground-based telescopes.

Keep ‘em peeled for more on this.

Ref:  arxiv.org/abs/0807.1316:  The MEarth Project: Searching for Transiting Habitable Super-Earths around Nearby M-dwarfs