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Cosmic Puzzles

April 26, 2012 by Frank Summers

cosmic puzzleSome folks assume that professional astronomers all had telescopes when they were kids; that they grew up memorizing constellations and facts about planets, stars, and galaxies; and that they got white lab coats for their ninth birthdays.

None of those are true about me. I got a bicycle for my ninth birthday, and I’ve never owned either a white lab coat or a telescope (unless binoculars count).

The reason I became an astronomer is that I am obsessive about solving puzzles. As a child in the 1970s, I loved playing with the Soma cube puzzle. When the Rubik’s Cube went on sale in 1980, I bought one the first day I heard about it. I twiddled, solved, and created patterns on it for many moons. I own every size cube up to a 7×7x7 — that’s seven squares in each row — including a 1×1x1 that a friend made for me, and dozens of other 3D rotating, flipping, and/or sliding puzzles.

Beyond those physical manipulation puzzles, I also love the intellectual challenge that many math students fear most: word problems. To me, equations are only really interesting when applied to a situation. Give me a description, let me deduce both the method and the solution, and I‘m hooked. In addition to baseball, I played at recreational math. I felt I lost a bit of my childhood when Martin Gardner, math and science writer best known for his Scientific American math puzzles, passed away a couple years ago.

So I came to astrophysics in a sideways fashion. I was brilliant at math, and the best math problems came from physics. As I progressed through college physics, the most interesting situations were in astronomy. What could be a greater puzzling challenge than to deduce all the physics of a situation trillions of miles away simply by examining the light it emits? And the answers described possibilities not only unheard of, but also impossible to reproduce here on Earth.

When speaking to students, I tell them it’s OK not to know what you want to be when you grow up. At one time, I dreamt of being a baseball pitcher. My experience says that if you work hard and follow your passion, you never know where it might take you.

It may say “astrophysicist” on my business cards, but really, I’m just a cosmic puzzle junkie.

A New Beginning

April 24, 2012 by Mario Livio

Blog: A Curious MindAfter a few years of writing postings for the “Speaking of Hubble” blog (and greatly enjoying it), I will be moving to a new platform in the blogosphere.

My new blog, “A Curious Mind,” is intended — you guessed it — for curious minds. I will be writing mostly about science, occasionally about art, sometimes about the connections between the two. These will be somewhat longer pieces, discussing topics at the forefront of science, and at the intersection of science and general culture. I will augment the blog postings with Tweets – you can follow me on Twitter, at Mario_Livio.

As you can imagine, as an astrophysicist at the Space Telescope Science Institute, Hubble and the upcoming James Webb Space Telescope continue to be front and center in my mind. Consequently, these topics will, no doubt, feature frequently in my postings and Tweets.

I am looking forward to this new literary adventure, and I can only hope that the readers will share my passion for science and art.

How Can Planets Get Their Water?

April 19, 2012 by Ray Villard
Artist’s view of super-Earth GJ1214b orbiting a red dwarf star

Super-Earth GJ1214b orbits a red dwarf star (artist’s view).

Over the past year there has been a string of breathless news stories about astronomers finding extrasolar planets in the habitable zone around their star. This is the “Goldilocks zone” where temperatures are not too hot, and not too cold, but just right for surface water to remain liquid and presumably nurture life as we know it.

Astronomers with the Search for Extraterrestrial Intelligence (SETI) are firing up their Allen Array telescope to check out these worlds for signs of intelligent life.

But using the term Earth-like for these planets is stretch at best, and misleading at worst. We don’t have a clue about the physical nature or processes on these worlds, any more than an air traffic control radar blip tells you what meals are being served on a commercial flight.

Saying that water could exist is OK, but to imply it does exist with the phrase “Earth-like planet” is very presumptive.

The bottom line is that we don’t know how Earth got tanked-up with its water supply. So how might we guess what’s happening on worlds thousands of light-years away?

“If we need exotic mechanisms to get water onto Earth, then maybe it suggests life is not prevalent in these exoplanetary systems,” says astrobiologist Karen Meech of the University of Hawaii.

The oceans account for merely one-quarter of one percent of Earth’s mass. Another one-tenth of a percent of water may be in Earth’s mantle. If we could probe deeper, down into the core, Earth could conceivably have 50 oceans worth of water locked away from the days of our planet’s formation. (This is somewhat bemusing, considering Jules Vern wrote about a great subterranean ocean in the 1864 “A Journey to the Center of the Earth.”)

With water potentially so locked away, “we may never know how much water Earth really has,” says Meech.

This complicates several competing theories for how Earth got its water supply in the first place. We know water is everywhere in the solar system, especially among the planets and moons of the outer solar system. They lie beyond the “frost line” where water can remain a solid. By comparison, the baked, rocky planets Mercury and Venus seem bone-dry, and Mars looks arid at best.

From the geologic record we do know that oceans were here on Earth just a few hundred million years after our planet’s formation 4.6 billion years ago.

Recent computer simulations show that all hell would have broken loose in our solar system if the outer planets had ever migrated in their orbits – a phenomenon commonly seen in exoplanetary systems that may also have happened here. Earth would have been pelted with water-bearing asteroids that were thrown into Earth-crossing elliptical orbits. This would explain a late, heavy asteroid bombardment 3.9 billion years ago, as recorded on the moon and other solar system bodies.

Or perhaps water was transported to the early Earth by a class of object that no longer exists? And did the water appear late, early or in intermediate episodes in Earth’s formative years?

The picture is so complicated that it’s safest to say that water came to Earth from many sources: comets, hydrated asteroids, solar nebula gasses, and chemical processing on Earth’s surface.

Because we don’t even know how much water Earth has, we don’t know if our planet is a comparatively dry or wet planet. Now astronomers using Hubble have found a new class of planet that may truly be a water world. Zachory Berta of the Harvard-Smithsonian Center for Astrophysics (CfA) and colleagues have uncovered a new class of planet where a very large fraction of its mass is water. A thick, steamy atmosphere enshrouds it. But don’t plan on going surfing; the surface temperature is 450 degree Fahrenheit.

The waterworld, called GJ1214b, is 2.7 times Earth’s diameter and orbits a red dwarf star every 38 hours at a distance of 1.3 million miles.

In 2010, CfA scientist Jacob Bean and colleagues reported that they had measured the atmosphere of GJ1214b, finding it likely that the atmosphere was composed mainly of water. However, a hazy atmosphere could also explain their observations.

The infrared capabilities of Hubble’s Wide Field Camera 3 were used to study the planet at infrared wavelengths when it passed in front of its star. The team essentially used Hubble to measure the infrared color of sunset on this world. Hazes are more transparent to infrared light than to visible light, so the Hubble observations help tell the difference between a steamy and a hazy atmosphere.

The astronomers found the spectrum of GJ1214b to be featureless over a wide range of colors. The atmospheric model most consistent with the Hubble data is a dense atmosphere of water vapor.

The planet could only have amassed so much water if the planet had formed farther away from its star, beyond the frost line where water ice would be abundant. The planet then migrated inward toward the star, either through friction with gas in the disk or by gravitational interactions with other planetary bodies.

In the process, the wandering planet would have passed through the star’s habitable zone. Therefore, long ago it would have had a balmy ocean like Earth’s. But was the planet there long enough for life to start? The water planet is a prime candidate for further observations with the infrared capabilities of the upcoming James Webb Space Telescope.

Data Exhaust

April 12, 2012 by Alberto Conti
The Hubble Deep Field (HDF) unveiled a myriad galaxies in 1995.

The Hubble Deep Field (HDF) unveiled a myriad galaxies in 1995.

Scientists in general, and astronomers in particular, have been at the forefront when it comes to dealing with large amounts of data. These days, the “Big Data” community, as it is known, includes almost every scientific endeavor — and even you.

In fact, Big Data is not just about extremely large collections of information hidden in databases inside archives like the Barbara A. Mikulski Archive for Space Telescopes. Big Data includes the hidden data you carry with you all the time in now-ubiquitous smart phones: calendars, photographs, SMS messages, usage information and records of our current and past locations. As we live our lives, we leave behind us a “data exhaust” that tells something about ourselves.

Does the universe contain some hidden data, data that is there in plain sight but has yet to be investigated? If so, what’s in the cosmos’ data exhaust?

In late 1995, the Hubble Space Telescope took hundreds of exposures of a seemingly empty patch of sky near the constellation of Ursa Major (the Big Dipper). The Hubble Deep Field (HDF), as it is known, uncovered a mystifying collection of about 3,000 galaxies at various stages of their evolution. Most of the galaxies were faint, and from them we began to learn a story about our Universe that had not been told before.

At the time, I was a young graduate student at the Ohio State University. I still remember very vividly how mesmerized I was by what our universe was telling us with just one image. I remember calculating the approximate total number of galaxies in the visible universe, assuming that the HDF was a representative patch of our universe: 100 billion. I ended up using that image for my first paper as a graduate student, looking for distant quasars in the HDF.

The HDF represented a tremendous achievement for science in ways that are still reverberating today. It initiated one of the many legacies of the Hubble Telescope: deep images showing infant galaxies in the early universe.

However, the HDF was also instrumental for a generation of young astronomers in another significant way. For the first time, an observation was deemed so important in order to address basic questions about the structure and evolution of the universe that it needed to be made available immediately to the astronomical community around the world. This, as well as the underlying science, was a game changer. Typically observations are released to the astronomical community after a proprietary period — typically 6 months or a year. This gives the astronomers who requested the observation time to perform their investigations. In this case, the HDF team took the unusual step of both swiftly preparing the observations for scientific study and releasing them without delay, thus allowing students and researchers alike to dive immediately into the science of the observation. The success of this decision paved the way for future observations to be released with similar speed.

So was the HDF unique? Were we just lucky to observe a crowded but faint patch of sky? To address this question, and determine if indeed the HDF was a “lucky shot,” in 2004  Hubble took a million-second-long exposure in a similarly “empty” patch of sky: The Hubble Ultra Deep Field (HUDF). The result was even more breathtaking. Containing an estimated 10,000 galaxies, the HUDF revealed glimpses of the first galaxies as they emerge from the so-called “dark ages” — the time shortly after the Big Bang when the first stars reheated the cold, dark universe. As with the HDF, the HUDF data was made immediately available to the community, and has spawned hundreds of publications and several follow-up observations.

Many more examples exist of “deep fields,” and in all cases it seems that if we look closely at an unobserved portion of our universe we discover more and more of its “data exhaust,” pointing us to the signatures of its origin.

The Hubble Deep Field started a revolution in the way we look at our universe but also in the way we access information. This trend exists to this day. Just a few days ago the European Southern Observatory (ESO) released the widest deep view of the sky ever made using infrared light. Once again an unremarkable patch of sky comes to life and reveals more than 200,000 galaxies!

This trend is not about to end. Over the next decade, astronomy will undergo dramatic changes. Missions like the Panoramic Survey Telescope and Rapid Response System (PanSTARRS) and the Large Synoptic Survey Telescope (LSST) will be able to survey the whole sky in just a few days, creating a 3D map of the universe. I personally cannot wait to see what we will find!

The Life Cycles of Stars

April 5, 2012 by Jason Kalirai
White dwarf stars reside in the ancient globular star cluster NGC 6397.

Hubble's sharp vision uncovered white dwarf stars in the ancient globular cluster NGC 6397.

As you stargaze over the next few weeks, keep in mind that most of those tiny points of light scattered across the sky are burning infernos of gas. These stars are very much like the Sun. Some are bigger and more powerful, and some smaller. But they are not constant. Stars change over time, and evolve into different states. Understanding this process of “stellar evolution” is my primary passion in astronomy, and was the focus of a meeting we just held at the Space Telescope Science Institute, “The Mass Loss Return from Stars to Galaxies.”

Stars are sort of like humans … They are energetic when young, “cool” when old, and kind of boring in the middle years. The most important property of a star that defines how it will evolve over time is its mass. A low-mass star, like our Sun, will slowly burn its hydrogen into helium, and remain in a state of equilibrium for billions of years. This is great for us on Earth, since it provides us with a stable environment. But in about 4 billion years, the Sun will expand and begin to lose its outer layers. During this stage, called the red giant phase, the Sun will be so large that it will encompass the Earth’s orbit around it, crisping our planet!

Unlike our Sun, more massive stars – about 10 times the Sun’s mass – will suffer a very different fate. These stars burn through their gas very quickly, like sports cars, and then blow up as supernova explosions. In doing so, the star experiences a very energetic death and sprays 90% of its material into its surroundings. Why does this matter to us if our Sun will never meet this fate? Because this spewed-out material from exploding stars is very important in the cosmic cycle of star and planet formation. All the elements heavier than hydrogen and helium are produced in the cores of these massive exploding stars. That includes everything you see around you, from the computer you’re reading this on to the skin on your body. Yes, you are made of “star stuff.” Our Sun and its planets formed in a region of space that had already been polluted by previous supernovae, and so these heavy elements exist here.

So what about the death of our own star? During one of the breaks at the meeting, I spoke with a colleague of mine about the end fate of the Sun. When we look at the nearby galaxy, we see beautiful stars in the “planetary nebula” phase of their life cycle. This phase only lasts for a short amount of time, during which the outer layers shed by the star – the “mass loss” of the meeting’s title – are illuminated by the hot and exposed core of the dying star, the white dwarf. The resulting pictures of these objects are among the most beautiful sights in the universe. My colleague and I asked ourselves whether the Sun would end its life in one of these states, but we concluded that it would be unlikely.

The Sun has a couple things working against it. First, it doesn’t have as much mass as some of the other stars that become planetary nebulae, so the stellar ejecta will be less dense. Second, because it has less mass, it will evolve more slowly than larger stars. By the time the core of the dying Sun is ready to light up the material around it, that material will be more dispersed. Both of these effects lead to an unlikely case for a bright illumination of the gas.

Eventually, after the outer layers have been shed, the remnant star of the Sun – the stellar cinder – will cool and dim as time passes. This type of white dwarf star is the final resting state of 98% of all stars. These dead stars are littered all across our galaxy, and they have incredible properties. First, having no nuclear fuel, they are extremely faint and hard to detect. Powerful telescopes like Hubble have, however, revealed large populations of these stars in the nearby galaxy. Second, these stars are very dense. Although the progenitor lost half (or more) of its mass, the core is very small – about the size of the Earth. The density of the star is therefore about a million times higher than the density of ordinary matter on Earth. A tablespoon of material from a white dwarf would “weigh” as much as a school bus. Finally, the composition of that core is largely carbon, an end product of helium burning in the progenitor star. So, a white dwarf is essentially highly compressed carbon. In other words, our Sun will end its life as a giant natural diamond!

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