The Red Light District Part 2: The Light Bulb Paradox

June 9th, 2008

I had a post over the weekend where I claimed that life on a planet around a type M star (see classifications here) would be like living in a red light district. Not the sex part, just the red light part. M stars are cool as stars go, around 3000 Kelvin or a bit less, and put out most of their energy in the near-infrared, invisible to humans. What visible light is emitted is heavily skewed toward long wavelengths — red light. Simple physics, right?

Well, James Nicoll reminded me of something I had conveniently forgotten. Your typical old-fashioned light bulb operates at about 3000 Kelvin and emits a spectrum an awful lot like an M star. They look white, don’t they?

Well, yeah. That’s true. But I have also looked at M stars through telescopes and those suckers sure look red.

I’m calling this the “light bulb paradox.” Why doesn’t light from a light bulb look red? Should it? When doesn’t a spectrum correspond to the color of an object?

I’m not completely certain, but I think I’ve got some insight and an explanation, although it’s a little outside my expertise.

First, some reference material.   Spectra of M stars, which, except for the very coolest M8 star do put out some blue light and do resemble the spectrum of an incandescent light bulb.     For good measure, let’s also have the efficiency of the human eye as a function of color, the spectra of the sky and sunset (and light bulbs, tungsten and “full-spectrum”).   Finally, a nice discussion of the perception of color.

OK, that’s a lot of stuff to get through.   The key to understanding the paradox lies in the perception of color.   The eye has different cells that respond to different colors (red, green, and blue, with some overlap equivalent to the bandpasses of filters we use in astronomy).   When all three are sufficiently stimulated, the color is regarded as “white.”   Light bulbs are intense enough that all three are sufficiently stimulated and they look white, even though the spectral shape of the tungsten filament is very similar to that of an M star in a telescope or a sunset, both of which definitely   appear as shades of red.   The red-detecting cone cells in these fainter light sources send a much stronger signal than those from the red and green cone cells.

So the key to the paradox is the intensity of the light.   Saturating all the varieties of color-detecting cone cells results in white.

So what of our hypothetical planet orbiting an M star?   It’s going to depend on the particulars of how bright and large the star appears in the sky.   Let’s take an Earth-sized planet with Earth-type temperatures, ballpark.     Let’s take a typical M star with half the temperature and half the radius of the sun.   That will make the star emit only about 1/32 as much energy as the sun (see discussion in wiki blackbody article).   This will mean that the planet has to be much closer than the distance from the Earth to the Sun (an astronomical unit).   Because the radiation follows the inverse square law, it’ll have to be about 1/6 (square root of 1/32) of an AU orbital radius, and the star will look about three times bigger across than the Sun in the sky (it’s about half the size, but six times closer).   Now, that’s not the only large effect, however, even though it does affect how intense the light will be as it will be spread out over an area ten times larger.   Another large effect is that the spectrum is peaked in the near-infrared, and the ratio of visible light put out by the M star to that of the sun is very small (governed by Planck’s Law, again see the wiki blackbody article).   Based on some plots, I’m estimating another factor of five or so, largest in the blue.

This means that the M star’s visible light surface brightness will be approximately 50 times fainter than the sun, with a larger factor at shorter wavelengths.

The discussion here suggests that the Sun at sunset is seen through 6-10 magnitudes of visual extinction at yellow colors, which corresponds to factors of a few hundred to a few thousand, order of magnitude, compared to the Sun at noon.   I can look at the sun at sunset and it looks pretty dang red.   If we let it get ten times brighter, that’s somewhere approaching sunset and I think the sun starts to look red before it gets all the way to sunset.

So, having said all this, I think it will come down to specific details.   This order of magnitude estimate seems to put us on the boundary between what’s going to look white and what’s going to look red.   The colors of plants and things and the quality of the sky and general lighting should be equivalent to what we see on Earth approaching sunset, but not quite there.   It should look different, but probably not quite as different as I indicated in my original post.

Let’s call living around an M star as the “almost sunset” district.

Apparently, James, I will do other people’s homework when they disagree with me!   You’re on your own for the moment with the Jovian moons.

Permalink | Tags: Education, General, Personal, Science, Science Fiction | 2 Comments »

Living Around an M-Star: the Red Light District

June 7th, 2008

NOTE: I’m keeping the below post as originally written. It will be superseded by a post to come as the issue is more complicated than I appreciated.

A friend of mine has a story coming out and wanted to doublecheck some issues of colors on a planet orbiting an M-star. My friend supplied me with a technical source:

http://www.giss.nasa.gov/research/briefs/kiang_01/ and the press release is at http://www.giss.nasa.gov/research/news/20070411/.

The thing is, these are terrible! I mean, technically they seem correct and very detailed, based on a paper in Astrobiology last year, but I have a PhD in astronomy and understand the science but I can’t tell what they’re claiming in any specifics. The pictures would be great if they actually specified what sort of planet/star they were talking about.

Well, let’s consider the case of an M-star at any rate, and I’ll give you my take. Stellar classifications depend on the mass and age of a star. The temperature/mass sequence is OBAFGKM (“Oh be a fine girl, kiss me!” is the mnemonic). An M-star is a very low mass star, a few tenths solar, that is much cooler. How cool? Maybe a couple of thousand degrees Kelvin, about 1/3 of the surface temperature of the Sun. A star this cool puts out most of its light in the near-infrared part of the spectrum, and almost no blue or ultraviolet light whatsoever. It doesn’t look white like the Sun. It looks red. This makes a big difference in what things would look like on the surface of a planet in the water zone of an M-star, vegetation or not.

Fred Pohl wrote an interesting novel called JEM I remember reading in my college days. It takes place on a planet orbiting Barnard’s Star, an M-star and things are red, red, red!

The atmosphere will scatter shorter wavelength light preferentially, like on Earth, but a late enough type M-star won’t have much. Compared to the star (which will look big compared to the Sun, if you’re in the water zone where temperatures will be higher), the sky will be more orange/yellow.

The planets can be of all sorts, including like those here on Earth, which do a lot of absorption at red wavelengths. They wouldn’t, I don’t believe, look very green. I suggest they’d look black.

This is a very complicated multidisciplinary problem to simulate, as we not only need to know about the spectrum of the local sun, the atmosphere and what it absorbs, how bright the light is and how dilated the eye, but also to incorporate the response of the eye. The eye sensitivity is peaked at green wavelengths. This is why green lasers, which usually have the same power as red lasers, look so much brighter.

I submit that the color pallet is going to be red, orange, maybe yellow, and black. Something that looks blue under a white light is going to look black under the red light of an M-star. For an experiment, get some red/orange party lights (easier to find at Halloween) and then go look at different colored items under that light. Try different light levels, too, as the eye is less sensitive to color at low light levels.

Under an M-star, the spectrum is limited. It’s like living in a red light district, literally.

Permalink | Tags: Education, Personal, Science, Science Fiction | 6 Comments »

Post-Starburst Galaxies

June 6th, 2008

Here’s a good write-up of some work related to mine that was also presented this week in St. Louis at the AAS meeting.   It involves post-starburst galaxies, whose relationship to post-starburst quasars isn’t entirely clear to me just yet (I’m planning a project that should help answer that question to my own satisfaction next year).   Their study of the most massive systems indicates that the starburst was   quenched very rapidly by nuclear activity from the central black hole — a quasar in its most active form.   My group and I will be reading the journal paper very closely in the near future.

Permalink | Tags: Personal, Science | No Comments »

The Importance of Science in our Lives

June 6th, 2008

Brian Green has an op-ed in the New York Times speaking about the personal importance of science in our lives.   It is a good article, and meaningful, in my opinion.   Science has enabled you to read this post, but it has also done so much more.   Reflect on that.

Sometimes I feel like I’m a lucky bastard who gets paid to play full time.    But that’s not true.   The value of science isn’t in the dollars or the results.   It’s in the quest, and the understanding.

I’ve spent hundreds of thousands of dollars of government money making incremental advances in understanding quasars.   To what end?   To every end.   This is the quest, to understand the universe, for the world.   Some one should be figuring this stuff out, and it costs what it costs.   It’s about more than making a living or the American Dream.   It’s about understanding who we are and our place in the universe.

I care about this.   It is important.   It does matter.   And it costs what it costs.   We need to know in a meaningful way, true things, and this is the way.   Let’s all enjoy it.

Permalink | Tags: General, Personal, Science | 18 Comments »

Return to the Moon? Good Idea or Bad?

June 4th, 2008

Gregg Easterbrook wrote an Atlantic June 2008 article “The Sky Is Falling” in which he argues for more attention to the issue of near-Earth asteroids, which I think are very much worth paying attention to. He also suggests that establishing a sustainable moon base is a waste of effort.

Do you agree?

My friend and fellow sf author Jeffrey Carver doesn’t think so. He’s written them a very insightful letter that I hope they’ll publish:

Dear Editor:

Gregg Easterbrook gets it half right in “The Sky is Falling” (The Atlantic, June 2008). He argues incisively for the need for those in the space community to take seriously the planetary threat of wayward asteroids and comets. NASA isn’t interested, as Easterbrook says, and the Air Force is hardly seizing on it with gusto, either. I spoke recently with a USAF officer whose job is strategic planning, and his unofficial comment was that the Defense Department could be considered criminally negligent in its failure to recognize planetary defense as a crucial part of its job description. If an asteroid-strike occurs (or threatens), are NASA and the Air Force just going to shrug and say “Not my job”? As Easterbrook says, that needs to change.

Where he gets it wrong is his dismissal of the return-to-the-moon program as a waste of money, detracting from other efforts. While balancing funding is always difficult (and the space budget is vastly smaller than most people think, accounting for only about half of one percent of the U.S. budget), a return to the moon could be a promising next step indeed. Learning to homestead other worlds is the next step toward what Captain Kirk famously called “the final frontier.” The point is not that a lunar base will be a launch point for a Mars mission–no one suggests that. It is that living on the moon will give us necessary experience for future exploration (to Mars and elsewhere), in a place where help is three days’ travel time away, not six to twelve months’ travel time. Further, a moon base could be the first place for serious mining of extraterrestrial resources, signaling the beginning of the end of humanity’s sole reliance on Earth-based metal and energy resources. Why mine minerals on the moon? Well, if you want to get metals into space–for example, to build satellite-based solar energy systems to beam nonpolluting energy to Earth–it’s potentially a lot cheaper and easier to lift tonnage from the low-gravity moon than from Earth, especially if you build solar-powered electric launchers for the purpose. This is a good argument for mining asteroids, as well.

This brings us back to the wayward asteroid and comet problem. While Easterbrook mentions several promising technologies, the best
long-term solution may be to build an infrastructure for living and working productively in space–not just one low-Earth space station, but a community of space habitations, complete with multiple, varied, and redundant transportation systems. Instead of hoping someone can get off a nuke to deflect one of those wayward asteroids, let’s build a permanent capability to move large objects in orbit. If a deadly ball of rubble comes along, we could nudge it away. If a metal-bearing asteroid comes along, we could move it to a parking orbit. Then, instead of watching it destroy our civilization, we could turn it into a mineral-lode, and put it to work building our new future in space.

By the way, I don’t work in the space program, or for the military or the government. I’m writing as a concerned citizen. My occupation is writer, and my latest novel, Sunborn, is forthcoming in the fall.

Thanks. –Jeffrey A. Carver

 Loading ...

Note: Originally this was just “return to the moon” rather than “establish sustainable moon base.”

Permalink | Tags: Science | 9 Comments »

Press Conference Experience

June 3rd, 2008

I overslept and almost missed it yesterday!   The traveling, stress, and lack of sufficient sleep caught up to me.   I made it over okay, with a couple of minutes to spare.   I wanted to make some adjustments to the slides and practice the talk again just before the actual event, but didn’t have time.

The actual experience was a little anti-climactic.   It had the look and feel of a panel at a science fiction convention, although we had clearer rules and slides to display as we talked.    The room was large, especially given that there were maybe 25 people in the room total, so it appeared a little empty.   I was happy to see Phil Plait, the Bad Astronomer, sitting off to one side — he’s great at conveying astronomy to the public.   There was a webcast of the slides and the audio went out to a conference call, so that the actual audience was likely much, much larger.   I talked with one reporter on the phone afterward, however, and she said that the audio quality was far from optimal.   There was a question and answer session following the presentations, and all of us received a number of queries.   It made me realize I hadn’t done as good of a job as I’d wished.   The easiest, most obvious thing I needed to do was to skip the nuance, and focus on what was the single main result: how key aspects of galaxy evolution do indeed seem to be driven by mergers and interactions, at least in the most massive systems.   The business about how we see post-starburst quasars in every stage from interaction to full-bore post-merger is an imporant but secondary result, and confusing to emphasize too much.

The presentation that seemed to get the most attention was Marc’s Seigar’s talk about how the tightness of spiral arms can be used as a way to estimate a galaxy’s central black hole mass.   That observation is much easier to make than others in high-redshift spiral galaxies than others.   Phil Plait has a nice post about it.

So I’ve seen our work online in a few places so far: Bad Astronomy, National Geographic, Kazinform, Softpedia, and my own University of Wyoming.   If you see it mentioned elsewhere, let me know!

Overall, I’d give myself a B or B-.   An A for effort for sure, but there wasn’t enough time to do a superlative job given how I was overcommitted this month.   I was exhausted yesterday, went to bed early and slept for 11 hours.   And while I’d just gotten over another cold, I seem to have come down with one this morning again.   When I was younger, no problem.   Now, any time I’m traveling, stressed, sleep-deprived, I seem to get the sniffles. I’m looking forward to getting home to Laramie to relax and get healthy.

Permalink | Tags: Education, General, Personal, Science | 1 Comment »

HUBBLE SPACE TELESCOPE SPIES GALAXY/BLACK HOLE EVOLUTION IN ACTION

June 2nd, 2008

FOR RELEASE: 9:30 AM Central Daylight Time, June 2, 2008

HUBBLE SPACE TELESCOPE SPIES GALAXY/BLACK HOLE EVOLUTION IN ACTION

A set of twenty-nine Hubble Space Telescope (HST) images of an exotic type of active galaxy known as a “post-starburst quasar” show that interactions and mergers drive both galaxy evolution and the growth of super-massive black holes at their centers. Mike Brotherton, Associate Professor at the University of Wyoming, is presenting his team’s findings today at the American Astronomical Society meeting in St. Louis, Missouri. Other team members include Sabrina Cales, Rajib Ganguly, and Zhaohui Shang of the University of Wyoming, Gabriella Canalizo of the University of California at Riverside, Aleks Diamond-Stanic of the University of Arizona, and Dan Vanden Berk of the Penn State University. The result is of special interest because the images provide support for a leading theory of the evolution of massive galaxies, but also show that the situation is more complicated than previously thought.

Over the last decade, astronomers have discovered that essentially every galaxy harbors a supermassive black hole at its center, ranging from ten thousand times the mass of the sun to upwards of a billion times solar, and that there exists a close relationship between the mass of the black hole and properties of its host. When the black holes are fueled and grow, the galaxy becomes active, with the most luminous manifestation being a quasar, which can outshine the galaxy and making it difficult to observe.

In order to explain the relationships between galaxies and their central black holes, theorists have proposed detailed models in which both grow together as the result of galaxy mergers. This hierarchical picture suggests that large galaxies are built up over time through the assembly of smaller galaxies with corresponding bursts of star formation, and that this process also fuels the growth of the black holes which eventually ignite to shine as quasars. Supernova explosions and their dusty debris shroud the infant starburst until the activated quasar blows out the obscuration.

Starbursts fade as they age because the more massive and luminous stars have shorter lifetimes before exploding as supernovas. There should be a phase, however, during which the fading starburst and the quasar can be seen simultaneously. In the late 1990s, Brotherton discovered a candidate for such a transition object, which possessed the spectral signatures of both a quasar and an older starburst.The actual burst of star formation, equivalent to a significant fraction of a Milky Way’s worth of stars, was already 400 million years old, hence the label “post-starburst” quasar. Hubble images of this single extreme and distant object showed that it was the remnant of a galaxy merger.

In order to find more of these rare post-starburst quasars, Brotherton and his Wyoming-based team turned to the Sloan Digital Sky Survey, the largest catalog of quasar and galaxy spectra in existence. Searching through a candidate list of 15,000 quasars, they identified the signatures of post-starbursts in some 600 objects.Through ground-based telescopes the objects just appear as smudges, without detail.

Brotherton and his team turned the sharp-eyed Hubble Space Telescope and its Advanced Camera for Surveys to observe a subset of these post-starburst quasars that had the strongest and most luminous stellar content.Looking at these systems 3.5 billion light-years away, Hubble, operating without the distortions of an atmosphere, can resolve sub-kiloparsec scales necessary to see nuclear structure and host galaxy morphology.

“The images started coming in and we were blown away,” said Brotherton. “We see not only merger remnants as in the prototype of the class, but also post-starburst quasars with interacting companion galaxies, double nuclei, starbursting rings, and all sorts of messy structures.”

Hubble snapped pictures of 29 post-starburst quasars in total, using a red-light filter that emphasized the starlight over the glare of the bluer quasar.

“These images provide us tremendous insight into the complexity of galaxy evolution,” said team member Dr. Rajib Ganguly.  “We see nuclear activity and post-starbursts simultaneously in systems from pre-merger to post-merger and in between.”

More work remains to characterize the physics properties of each object, such as the masses and ages of the post-starbursts and the masses and fueling rates of the black holes powering the quasars. This task will require the combination of the Hubble images with high-quality spectra from the Keck Observatory on Mauna Kea, Hawaii, which team member Gabriella Canalizo has obtained. This more detailed work should provide additional insights into this phase of galaxy evolution.

Astronomers have determined that our own Milky Way galaxy and the great spiral galaxy of Andromeda will collide three billion years from now. This event will create massive bursts of star formation and most likely fuel nuclear activity a few hundred million years later. Hubble has imaged post-starburst quasars three and a half billion light-years away, corresponding to three and a half billion years ago, and three and a half billion years from now our own galaxy is probably going to be one of these systems.

This work is supported by grants from NASA, through the Space Telescope Science Institute and the Long-Term Space Astrophysics program, and the National Science Foundation.

Figure 1. JPEG thumbnail below. Red-light images of post-starburst quasars taken with the Hubble Space Telescope using the Advanced Camera for Surveys (ACS). Each image is ten arcseconds on a side, corresponding to a physical scale of approximately 120,000 light-years given the 3.5 billion light year distances of these objects.

Three individual post-starburst quasars on their own from the above mosaic:

Permalink | Tags: Personal, Science | 8 Comments »

Post-Starburst Quasar Press Release/Conference Coming Monday Morning

June 1st, 2008

A few weeks ago I mentioned I’d been asked to participate in a press conference regarding my research at the American Astronomical Society meeting in St. Louis.   Well, that happens Monday morning.   I’ll be posting the press release here to coincide with the press conference and will post about my experience afterwards.   I’m hoping it will be positive and a win-win for me, reports, and fans of science.

Permalink | Tags: Education, Personal, Science | 1 Comment »

Follow-Up on the Academic Ponzi Scheme

May 30th, 2008

I should have known that some astronomer would have already tackled, quantitatively, some aspects of what I discussed as an “Academic Ponzi Scheme” a few weeks ago.   Travis Metcalfe wrote a paper last year which is publically available here.   Here’s the title and abstract:

The Production Rate and Employment of Ph.D. Astronomers

Authors: Travis S. Metcalfe (NCAR)

(Submitted on 17 Dec 2007 (v1), last revised 19 Dec 2007 (this version, v2))

Abstract: In an effort to encourage self-regulation of the astronomy job market, I examine the supply of, and demand for, astronomers over time. On the supply side, I document the production rate of Ph.D. astronomers from 1970 to 2006 using the UMI Dissertation Abstracts database, along with data from other independent sources. I compare the long-term trends in Ph.D. production with federal astronomy research funding over the same time period, and I demonstrate that additional funding is correlated with higher subsequent Ph.D. production. On the demand side, I monitor the changing patterns of employment using statistics about the number and types of jobs advertised in the AAS Job Register from 1984 to 2006. Finally, I assess the sustainability of the job market by normalizing this demand by the annual Ph.D. production. The most recent data suggest that there are now annual advertisements for about one postdoctoral job, half a faculty job, and half a research/support position for every new domestic Ph.D. recipient in astronomy and astrophysics. The average new astronomer might expect to hold up to 3 jobs before finding a steady position.

Basically, he’s putting hard numbers on my qualitative discussion.   Check it out.

Permalink | Tags: Science | 1 Comment »

Errors in New Indiana Jones Movie

May 29th, 2008

As reported here.   Not science mistakes, which is my usual area, but apparently gross errors confusing Mexico and Peru, Mayans and Incas, and related issues of culture, language, and geography.   I understand the average movie-goer won’t care, but I also think that consistently underestimating the public helps reinforce negative attitudes toward education.   I mean, if these guys spending a hundred million dollars making a movie can’t bother to get things right, then why should anyone care?

Permalink | Tags: Education, Popular Events | 2 Comments »

Tenure

May 29th, 2008

Yesterday I was going through the mail I’d missed while I’ve been traveling, and came across the official letter finally that I am being promoted to Associate Professor with tenure on July 1, 2008, the start of our fiscal year.

Woo hoo!

So I knew this was happening.   My department and department chair all supported me, the Dean was very positive, the Tenure and Promotion Committee was unanimous, as were the overseeing administrators.   But still…it’s nice to have it official in black and white.

I covered some basics about tenure a couple of months ago when I wrote about “What Do Astronomy Professors Do.”   I’ll copy the parts regarding tenure below:

And let me explain a few things about tenure, what it means, and what it doesn’t.   Generally most new professors are technically “assistant professors,” who are regularly reviewed and can be dismissed easily if they’re not performing at expected levels.   Usually they’re given six years to meet that standard, and then they’re promoted to associate professor and given tenure, or fired (with a year to make a transition).   There’s a final level of full professor above associate that requires a tenured professor to continue to show high performance levels.

So about tenure…it is job security of a sort.   It makes firing a professor very difficult, and is meant to protect us and let us follow our research where ever it leads, even if it is offensive to some or just something that others think is a waste of time pursuing.   We can still be fired for the usual reasons someone would get fired (e.g., gross underperformance, etc.), but there’s a legal procedure that must be followed and a lot of corrective steps before those are reached.   I’m generally in favor of tenure (certainly for myself!), but it has pluses and minuses.   Some professors become what we call “dead wood” after getting tenure.   They teach their classes, putter about, but don’t continue doing significant new research or contribute to a department in serious ways.   Some do spend the last years of their careers pursuing bogus research that never pans out.   Sometimes though, it does let someone do something like a major long-term project that doesn’t bear fruit for many years, something that junior people trying to land jobs can’t afford to do.   That’s a good thing.

There.   A few minutes of happy glow have to be enough for today with so much to do.   Back to the salt mines now, as an old friend of mine used to say.

Permalink | Tags: Education, Personal, Science | 7 Comments »

Great Mind-Meld I Missed: Scientific Accuracy in Stories

May 29th, 2008

Over at www.sfsignal.com here.   Just plain missed it last week while I was traveling, which is dumb of me since sfsignal is one of the best sites to keep up with the science fiction world.

MIND MELD: Scientific Accuracy in Stories

Science fiction would be nothing without the science. Who doesn’t like reading about new or interesting ideas inside of a story? But should SF authors know their stuff when it comes to the science behind the stories? To that end, our question this week:

Q: Do science fiction authors have an obligation to be scientifically accurate with their stories? Is there a minimum level of accuracy an author should adhere to?

I like the answers by Alastair Reynolds, Alexis Glynn Latner, and Elizabeth Bear, although I don’t perfectly agree.   Nancy Kress’s point is good one, too.   I’ll be the hardass here.   If you’re writing science fiction, know your science.   This is no different from writers of historical fiction knowing thir history, or writers of any type doing enough research to know what they’re writing about.   I don’t have any problem with people coming up with new, undiscovered science, or anything else, as long as it doesn’t violate what we already know about how the universe works.   Then you’re just writing fantasy, which is fine, or being ignorant, which isn’t.

Permalink | Tags: Education, Science, Science Fiction | 2 Comments »