Thursday, May 30, 2013

A Book About the Mostly Invisible Universe

I assert that "Your Ticket to the Universe" by Kim Arcand and Megan Watzke is an outstanding book and you should consider buying it.


I'll give some reasons why, in no particular order (and I'll also discuss two of my favorite topics, the dark universe and multi-wavelength images):
Top: Saturn, as seen by Cassini. CreditCassini Imaging TeamSSIJPLESANASA
Bottom: the Bullet Cluster, from Chandra, HST, Magellan and ESO WFI data. Credit: X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.
  • It covers the Universe, ranging from bacteria on Earth up to the cosmological mysteries of dark matter and dark energy.
  • It has a tongue-in-cheek trailer:

  • Well-regarded writers and astronomers said very complimentary things about the book:
 "This is the "Goldilocks" book for a reader who wants more than pretty pictures, but less than a treatise on astrophysics. It's a great "ticket" to that space in-between the coffee table book and the text book. Just enough extra information to understand why these beautiful images of the Universe matter, to us all."
Dr. Alyssa Goodman, Harvard professor of astronomy
"A delightful jaunt through space and time, equal parts knowing verve and dazzling views.”
- Dan Vergano, USA TODAY 
"The Universe is the ultimate ride, and this book is your ticket to get on. Arcand and Watzke use gorgeous images as well as clear, easy-to-understand prose, so you'll really enjoy the view as you travel from Earth to infinity."
- Dr. Phil Plait, Astronomer and author (badastronomy.com)
  • Astrophysicist Mario Livio, an accomplished author himself, wrote a very positive foreword.
The Cats-Eye nebula (aka NGC 6543), as seen with Chandra and HST. Credit: X-ray: NASA/CXC/RIT/J.Kastner et al.; Optical: NASA/STScI

Reasons not to buy the book:
  • You cannot afford the (US) $24.95.
  • You're a troll, crank or conspiracy theorist who harbors deep distrust about all the invisible things astronomers love to study, like black holes, dark matter and dark energy, topics that are covered in "Your Ticket to the Universe" in some detail. I give more comments about this below.
  • You're a troll, crank or conspiracy theorist who is suspicious about images that show the electromagnetic spectrum beyond the optical range. "I've got to see it to believe it", they might say, but this is radiation that we cannot see. "Your Ticket to the Universe" is full of multi-wavelength images. Again, I give more comments below.

There may be other reasons not to buy the book, but I can't think of any (full disclosure: Kim Arcand and Megan Watzke are friends and colleagues of mine). So here it is on Amazon.

Authors Kim Arcand (left) and Megan Watzke (right). Credit: Adeline and Grace Photography

As promised, I'll elaborate on two of the points raised above, about the dark universe and multi-wavelength images.

The Dark Universe

When I think about people who don't believe in black holes, dark matter or dark energy I'm mostly referring to self-trained "scientists" who have read a few popular science books, have developed an unhealthy dose of skepticism and like to concoct their own theories. These people are difficult to argue with and usually aren't interested in hearing about evidence that contradicts their suspicions. They can be found lurking in the darker corners of the internet and sometimes contact astronomers to share their research.

There are also real scientists who are skeptical about the darker side of astronomy. In researching this post I was reminded that Lawrence Krauss has argued that black holes might not be able to form. He's not the only scientist who is skeptical. For example, another physicist has argued that the objects astronomers think are black holes are really dark energy stars. (Physicist and science writer Matthew Francis has argued against this idea.) However, the majority of astronomers do think that black holes exist. In some cases the evidence is very strong, including one that involved a bet between Stephen Hawking and Kip Thorne about whether a black hole really exists in Cygnus X-1.

A Digitized Sky Survey (DSS) optical image showing the black hole Cygnus X-1 (left) and an artist's illustration (right) showing a close-up of the black hole. Credit: Optical: DSS; Illustration: NASA/CXC/M.Weiss

There are also some professional scientists who are skeptical about the existence of dark matter and dark energy, as Charles Choi has written about here and here. "Your Ticket to the Universe" does not attempt to cover all of the different pieces of evidence for dark matter and dark energy, but it mentions a few.

Although most astronomers are comfortable with the "standard" model of cosmology, with dark energy and dark matter dominating the mass-energy of the Universe, modifications to gravity are taken seriously as a possible explanation of the accelerating expansion of the Universe and an alternative to dark energy. The Nobel Committee were careful in awarding their 2011 Physics prize to Adam Riess, Brian Schmidt and Saul Perlmutter "for the discovery of the accelerating expansion of the Universe through observations of distant supernovae", not for discovering dark energy. Attempts to explain away dark matter by modifying gravity aren't nearly as well motivated, but that's a subject for another blog post. As Jim Peebles, a leading cosmologist, says in a recent paper: "The evidence for the dark matter of the hot big bang cosmology is about as good as it gets in natural science." 

Multi-wavelength images

Besides multi-wavelength images, another red flag for some skeptics are images that have been processed with Photoshop. If this program can make models look skinnier, or correct blemishes, maybe it can do the same with galaxies. Scandalous! Photoshop was used in many of the images in "Your Ticket to the Universe" and it's the tool of choice for combining different wavelengths. The only "touching up" that occurs is repairing image artifacts, equivalent to fixing the red eye in photos that use a flash. The crucial tool in Photoshop is being able to overlay multiple images with different wavelengths.

Earlier this year, MIT Professor Tom Levenson wrote a blog post about a couple of people who believe that the coloring used in multi-wavelength images is "propaganda with which NASA and space scientists in general trick us into paying for the observatories in space and on earth that generate the data behind the fibs." Judging from their comments, this pair qualify as trolls and cranks and conspiracy theorists. Levenson gave an excellent defense of the power of multi-wavelength astronomy and used a Chandra and Hubble image of Eta Carinae that appears in "Your Ticket to the Universe".

A composite image of Eta Carinae combining data from Chandra and Hubble. Credit: X-ray: NASA/CXC/GSFC/M.Corcoran et al.; Optical: NASA/STScI 

One minor criticism of Levenson's article is that he uses the term "false color" to describe images outside the optical spectrum. This is a term that's commonly used by scientists, but the astronomers who are image experts tend to avoid it. As astrophysicist and image expert Robert Hurt from JPL said in a blog post "I personally dislike that term a lot because it implies something is being misrepresented." Another astrophysicist and image expert, Travis Rector, from University of Alaska, noted in a paper in The Astronomical Journal:
"Terms such as "false color" and "pseudocolor" are often used to describe images assembled with other methods, implying that such images are fabricated. However, the goal of these images is data visualization, not a portrayal of reality as defined by human vision. Color and intensity scaling therefore serve a different role."
His footnote to the first sentence described above is:
"In reality no astronomical image accurately represents the appearance of an object, as the human eye's sensitivity to color is very complex and nonlinear. Ultimately such arguments are rhetorical, as the purpose of a telescope is to show what the eye cannot see."
What observatories like ChandraHubble, the Spitzer Space Telescope, and the Very Large Array give us is a type of *superhuman* vision, containing rich scientific detail and often dazzling beauty. It's churlish and ignorant to describe it as propaganda. As for being a trick, the image experts at the Space Telescope Science Institute have been very open about how they make their images and the same applies to our Chandra image expert Joe Depasquale who wrote a blog post a few months ago about how he made an image. There is also an excellent article in Slate by Daniel Engber giving a detailed explanation about how astronomical images are made. I like everything about this article except the title and subtitle, which plays on the popular notion that Photoshop is about fakery. Advice for it was provided by Robert Hurt and astrophysicist Frank Summers from Space Telescope Science Institute.

Kim and Megan have also written at Huffington Post about the meaning of color in astronomical images, and you won't see any mention of "false color"in their blog post.

If you're so inclined, there are also detailed instructions on how to make your own color images using the processed data. Here are the instructions provided by the Hubble image experts, and those from the Chandra image experts. This recent video also includes Hubble image expert Zolt Levay discussing how their images are made.


You might think I'm reacting strongly to the criticism of only two trolls, but I did some research and found a broader mistrust of images, including science journalists and astronomers. I'll leave the details to a follow-up blog post, where I'll give some examples of these complaints and explain the production of a few classic images.

A composite image of W49B containing Chandra data (blue and green), VLA data (pink) and Palomar Observatory data (yellow). Credit: X-ray: NASA/CXC/MIT/L.Lopez et al.; Infrared: Palomar; Radio: NSF/NRAO/VLA

I'll end on a positive note, by showing an image that's too new to be included in "Your Ticket to the Universe". The subject of Joe Depasquale's blog post, W49B, provides another powerful demonstration of the benefits of multi-wavelength observations. The X-ray, infrared and radio data combine to make a beautiful image with exciting science, but the optical image, as Joe explains, shows nothing. The universe is a much more interesting and beautiful place when we observe it with everything we've got. This is the spirit of "Your Ticket to the Universe".

Thursday, May 23, 2013

Kepler, Exoplanets and Dark Matter in the News

NASA's Kepler mission is not doing well.  Its planet-hunting days are probably over because one of its reaction wheels failed and it cannot point accurately anymore. The research isn't finished because the data in the archive still has to be analyzed and follow-up observations from ground-based telescopes will carry on for years, but this problem is obviously disappointing news.

Here, I'll discuss the strong public interest in Kepler's planet results and the widespread media coverage that's been generated. It's like the scientists have been playing a game to one-up each other, as more and more records have been broken for the smallest planet, or the planet that's most likely to be hospitable to life, and so on. These gains occurred naturally, as the length of the mission increased and the ability to detect small planets in the habitable zone improved (later in the article I'll comment about the difficulties with the term "habitable zone").

The results released in April are a good example of this. The release was about planets in the habitable zone, where liquid water may exist. Because at least three transits are needed to identify a planet, and objects in the habitable zone of stars similar to the Sun can have periods of hundreds of days, these results could not have been obtained early in the mission.

The artist's concept depicts Kepler-62f, a super-Earth-size planet in the habitable zone of a star smaller and cooler than the sun, located about 1,200 light-years from Earth in the constellation Lyra. Kepler-62f orbits it's host star every 267 days and is roughly 40 percent larger than Earth in size. The size of Kepler-62f is known, but its mass and composition are not. However, based on previous exoplanet discoveries of similar size that are rocky, scientists are able to determine its mass by association. Caption from Kepler web-site.
Credit: NASA/Kepler Mission.

This work, led by the Kepler PI Bill Borucki, is excellent for publicity. The Science paper, titled "Kepler-62: A Five-Planet System with Planets of 1.4 and 1.6 Earth Radii in the Habitable Zone" contains strong claims and superlatives:
"Therefore Kepler-62e and -62f are Kepler’s first HZ planets that could plausibly be composed of condensable compounds and be solid, either as a dry, rocky super-Earth or one composed of a significant amount of water (most of which would be in a solid phase due to the high internal pressure) surrounding a silicate-iron core."
and
"With radii of 1.61 and 1.41 [solar radii] respectively, Kepler-62e and -62f are the smallest transiting planets detected by the Kepler Mission that orbit within the HZ of any star other than the Sun."
With statements like this, it's easy to see that the title of the press release, "NASA'S Kepler Discovers its Smallest 'Habitable Zone' Planets to Date" is justified by the paper.

Dark Matter Hints?

Sometimes there can be a big difference between the claims in the science paper and those in the press release, leading to problematic media reports. Jumping from exoplanets to cosmology, here's a recent example concerning results from the Alpha Magnetic Spectrometer (AMS). Concerning their detection of an excess of positrons with AMS, the press release says:
"These results are consistent with the positrons originating from the annihilation of dark matter particles in space, but not yet sufficiently conclusive to rule out other explanations."
AMS in orbit on the Space Station photographed on July 12, 2011. Credit: NASA/AMS-02 collaboration.

Even saying they might have detected dark matter is a strong claim. So, what does the science paper say about dark matter? Explicitly, nothing. That's not completely true because reference [2] mentions "Proceedings of the Tenth Symposium on Sources and Detection of Dark Matter and Dark Energy in the Universe, Los Angeles (to be published)", but that hardly counts. The closest the text of the paper comes to mentioning dark matter is in the final sentence before the acknowledgements:
"These observations show the existence of new physical phenomena, whether from a particle physics or an astrophysical origin."
That's a vague statement, and the resulting press coverage was not terrific. Dark matter expert Katie Mack gave an excellent summary in her article "Space Station's Detector Has Not Found Dark Matter, Despite What Some Media Reports Say" at the new blog Physics Focus. One article I spotted
starts with this sentence:
"Physicists announced on Wednesday that they have discovered the most convincing evidence yet of the existence of dark matter – the particles that are thought to make up a quarter of the universe but whose presence has never been confirmed."
This sentence is problematic because much better pieces of evidence have been found for dark matter, including cosmic microwave background observations (CMB) by WMAP released in 2003, Planck CMB results released earlier this year, and observations of the Bullet Cluster with ChandraHST and other telescopes.

This composite image shows the galaxy cluster 1E 0657-56, also known as the "bullet cluster", formed after the collision of two large clusters of galaxies. Hot gas detected by Chandra is seen as two pink clumps in the image and contains most of the "normal" matter in the two clusters. An optical image from Magellan and the Hubble Space Telescope shows galaxies in orange and white. The blue clumps show where most of the mass in the clusters is found, using a technique known as gravitational lensing. Most of the matter in the clusters (blue) is clearly separate from the normal matter (pink), giving direct evidence that nearly all of the matter in the clusters is dark. This result cannot be explained by modifying the laws of gravity. Caption taken from this web-site.
Credit
X-ray: NASA/CXC/CfA/M.Markevitch et al.; Optical: NASA/STScI; Magellan/U.Arizona/D.Clowe et al.; Lensing Map: NASA/STScI; ESO WFI; Magellan/U.Arizona/D.Clowe et al.

Use of "but whose presence has never been confirmed" can also be a problem because some people might infer that it has now been confirmed.

I think a substantial amount of the responsibility for articles like this lies with the AMS publicity effort and the large disparity between the paper and the press release. Use of the term "consistent with" in the release is especially problematic, because the scientific use of this term (not inconsistent with) differs from the use that most people assume (agrees with). To use an extreme example, one could also say that the observations are consistent with invisible fairy dust or alien exhaust fumes. It's a term that's best avoided.

Astrophysicist and writer Ethan Siegel gave a detailed explanation of the AMS result and a forceful critique of the publicity effort, arguing that the press release and press conference were misleading and even deceitful.

This is not easy work to explain. The results from the various attempts to detect dark matter directly are very complicated and often seemingly contradictory, as Katie Mack points out in another excellent blog post. With their large workloads, science writers need all the help they can, especially the ones who don't specialize in astronomy.

The Three S's

The contrast with Kepler research is stark. Kepler has three great strengths regarding publicity: simplicity, success and sexiness. The way Kepler works - finding transits - is simple and easy to understand. Clearly, Kepler been very successful at finding planets, or more specifically planet candidates. Finally, the search for planets is, in my opinion, sexy science, in part because of the connection to finding life. So, Kepler has some clear advantages over dark matter detection work.

These light curves of Kepler's first five planet discoveries show not only drop in star brightness as the planet transits the star, but an indication of the planet's inclination--how far from the center the planet is passing across the star. Caption taken from this web-siteCredit: NASA/Kepler Mission

Although astronomy publicity is renowned for beautiful images, Kepler hasn't had them and hasn't needed them. However, it has inspired some outstanding animations, visualizations and illustrations. Examples are these videos from the Kepler team available here and here and this graphic from the New York Times.

But, there have been some challenges. Kepler has been so popular with the media that it has led to discussion about whether there has been too much exoplanet news. Here's a very interesting blog post by John Rennie titled "Exoplanets bore me (and what that means for science news)", with some particularly good discussion between Rennie and astrophysicist August Muench.

There are also challenges involved with reasonable use of "habitable zone" and "Earth-like planets". I've already used "habitable zone" freely in this article but the concept involves many subtle details. An audience member during "The Great Exoplanet Debate" mentioned that it would be great if astronomers could keep discovering habitable planets and MIT astrophysicist Sara Seager interrupted to say:
"Hold on. Let me just interrupt. There's a correction involved here. That is: people keep claiming the first habitable planet, and as far as exoplanet astronomers go, there's no agreement that there's any habitable planets."
If the experts can't agree on whether there are any habitable planets then you know it's a term to approach with caution. Earlier, Seager advocated use of "potentially habitable" to make it clear that they are making educated guesses.

Astrophysicist John Johnson describes the challenge nicely by explaining that its almost impossible to know if a planet is truly habitable. This is because "we don't even know the conditions for habitability on our own planet!". He then gives a long list of factors or questions that may or may not have been significant for the development of life on Earth, following a discussion with fellow exoplanet expert Jason Wright.

As astrophysicist and writer Matthew Francis explains in a blog post:
"Habitability is a complex and fascinating notion, and of course until/unless we discover life on another world, we can’t be absolutely certain what conditions are truly “just right”."
Then there's the issue of "Earth-size" vs "Earth-like" planets. As Seager explains,
"Those are two very different concepts. And its almost impossible to communicate that. Even professionals slip up. Earth-like means it’s like Earth, with oceans and land and trees and everything great. Earth-size could be anything. It could be hotter than anything that you could imagine and be Earth-size."
Science writer Lee Billings has also written about the challenges of defining Earth-like planets, and astrophysicist and writer Caleb Scharf has asked whether we should expect other Earth-like planets at all.

Kepler hasn't been the only observatory to make major contributions in exoplanet research. The early work was dominated by radial velocity studies - the "wobble" method - and more recently there have been notable observations using this technique. However, Kepler has inspired much of the debate and discussion described above. This discussion will continue as new results are pulled out of the Kepler archive and astronomers keep using ground-based facilities to search for exoplanets. The next dedicated effort from NASA will be the Transiting Exoplanet Survey Satellite (TESS) and the James Webb Space Telescope (JWST) should also make big advances.

Sizes of planet candidates found with Kepler. The percentages in yellow show the changes in the numbers of planet candidates in different categories, when comparing the January 2013 and February 2012 catalogs.
Credit: NASA/Kepler mission

The exoplanet field has been active for less than 20 years, but has expanded enormously in that period, especially in the Kepler era. Astronomers have been surprised by what they've found many times. The detection of planets around pulsars was a surprise as was the early detection of hot Jupiters. More recently the detection of large numbers of "super Earths", with masses sizes between Earth and Neptune, has been surprising, along with the large diversity in planet characteristics. It will be fascinating to see what else can be found with Kepler and with future observations.

Exoplanet Publicity in the Future

It's difficult to predict where exoplanet science will go in the future, but I'm confident that public interest will increase. Although some writers might feel that planet news reached saturation levels, I think there's room for growth. As an informal demonstration, I've played around with Google Trends showing how terms used in Google web searches have changed with time. The numbers here should be treated with caution, as there can be multiple uses of the same search term, and I haven't spent a long time experimenting with this tool.

The first plot here shows the recent increase in searches containing "exoplanet" and "habitable zone", compared with a flat curve for "black hole galaxy". (I include "galaxy" to place limits on the results for "black hole". I found that other variations are also flat, but with different normalizations. I also excluded terms for "exoplanet" because of searches unrelated to planets).

In the next plot I kept the same search term for "exoplanet" but searched for "black hole" by itself, without "galaxy". I replaced "habitable zone" with "new planet" and I added two other search terms, the fictitious planet "Nibiru" and "Pluto planet". I restricted this search just to the US, so that the results for "Nibiru" are not exaggerated because the term is used in different languages. You can see the blue line for "exoplanet" now almost disappears because it is so small. Part of the issue is that the Kepler results are still relatively new and the terminology may not have sunk in.

What are all the peaks? The peak for "Pluto planet" occurred in August 2006 when the IAU voted to reclassify Pluto into a dwarf planet and the peak for Nibiru occurred at the end of 2012 because it was identified as a potential culprit for the end of the world. The peak for "black hole" occurred in September 2008 when the Large Hadron Collider (LHC) turned on and some people were concerned that a black hole would be created and destroy the Earth. One conclusion is that fanciful threats to the Earth and votes that cause changes in textbooks generate a lot of interest. (*)

The peaks in "new planet" correspond to announcements for the discovery of the dwarf planet Sedna in March 2004, Xena and other dwarf planets in July 2005, the exoplanet Gliese 581c in April 2007, the exoplanet Gliese 581g in October 2010, and the exoplanet Kepler-22b in December 2011.

These peaks are reasonably large. For example, they are comparable to the size of peaks for "climate change" and, for the last couple of years, to "global warming", a term that's declining in use. In the plot shown here they are the only strong peaks corresponding to new scientific results, showing the high public interest in planets. It's notable that all five of these popular stories correspond either to new objects in our solar system or the discovery of new exoplanets that may harbor life. A discovery like the possible planet around Alpha Centauri B - announced in October 2012 - received less attention, perhaps because that exoplanet is much too close to its star to be habitable.

To place these results in perspective, I replaced "pluto planet" with "beer" and this time the other search terms are so small they almost disappear. I'm not sure interest in exoplanets will ever consistently rival interest in beer, but as I said earlier, there's room for growth. Interest in planets is high when discoveries are made, but it's not obvious that this level is sustained.

There are many exciting fields in astronomy, including black holes, supernovas and cosmology, but exoplanet work has the potential to capture public interest in an unprecedented way. Astronomers are already starting to predict that biosignatures may be detected in exoplanets not too many years into the future, and such a discovery would surely surpass the interest shown in far-fetched speculation about mini-black holes in the LHC. If we find life outside the Earth it would change our view of life on Earth for ever.



(*) One interesting aspect of the results is that the terms for "exoplanet" and "habitable zone" have high search rates in just a few populous states like California and New York. For the other more popular terms there are high search rates across almost all of the US.