[Koji's blog] Light Echoes around a Mysterious Nova

“In 1890 T Pyxidis had appeared, brightened, and disappeared. When I first came to Harvard they were still telling how it was found again during a routine survey of plates taken in 1919, and how Miss Leavitt exclaimed: ‘That star hasn’t been seen for almost thirty years!’ – the first recurrent nova to be discovered.”

- Cecilia Payne-Gaposchkin in Fifty Years of Novae

Henrietta Swan Leavitt in the above quote is well known for discovering the period luminosity relationship of Cepheid type variable stars, which has since become an essential rung of the cosmic distance ladder. Cecilia Payne-Gaposchkin may be less widely known, but her contributions are arguably even more important than those of Leavitt’s (try typing “the most brilliant Ph.D. thesis ever written in astronomy” in to your favorite search engine). Years after her thesis work, Payne-Gaposchkin turned her attention to novae, and thanks to brilliant scientists like her, we know a lot about these explosions. Yet there is still much about novae that we don’t understand, and most nova researchers would agree that T Pyxidis (or T Pyx for short) is the most puzzling of them all, recurrent or otherwise.

April 15, 2011 outburst of T Pyxidis
Animation courtesy of Ernesto Guido and Giovanni Sostero

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[Koji's blog] A Victorian Scandal

A recent event reminded me of a scandal of a sort that happened around 1850. At the center of it was John Russell Hind, a British astronomer (I mentioned him in a previous blog about archives).

Hind was a superb observer who knew the sky very well. He discovered many interesting objects outside the solar system, but his main passion was the discovery of asteroids. He ended up discovering 10 of the first 30 asteroids known, which is quite a feat considering how hot this field was at the time. As the discoverer, he got to name these asteroids. At the time, asteroid names were picked from mythology – such as Ceres, Pallas, Juno, and Vesta, the names of the first 4 asteroids known.

Hind named the first two asteroids he discovered (nos. 7 and 8 overall) Iris and Flora. These sound more like old-fashioned women’s names to me, but they certainly are names from classical mythology, and so they passed without comments. Hind then picked the name “Victoria” for one of his later discoveries.

There was a reaction to this choice: “we are not amused” would be one way to put it. “You can’t name an asteroid after *your* queen,” would be another. Hind claimed, however, that he took the name from Roman mythology, in which Victoria is the goddess of victory. It was pure coincidence, according to him, that his sovereign, the Queen of the British Empire, was also called Victoria.

This composite image shows the comparative sizes of eight asteroids. Credit: NASA/JPL-Caltech/JAXA/ESA

Fast forward 160 years or so. Recently, there was an internet poll to pick the names of a couple of small moons of Pluto. The clear winner: Vulcan. Some people said “you can’t name a moon of Pluto after a Star Trek planet.” (Sounds familiar?) Others countered
“but Vulcan is the god of fire in Roman mythology.” (Sounds familiar?) Some things never change, or so it seems, including the name of the asteroid no. 12 – still called Victoria, despite the initial objections.

So, the Star Trek connection probably will not disqualify the proposed name, Vulcan. Still, I’m not a big fan of this pick – wouldn’t you rather name a much hotter world after the god of fire, like one of the “hot Jupiters”?

Right now, exoplanets have relatively boring names – designated with lower case “b”, “c” etc. after the name of the parent star. Things could get very interesting, if astronomers ever decide to give them proper names.

Pluto and moons
Pluto and its moons, as seen by the Hubble Space Telescope, Credit: NASA, ESA, and L. Frattare (STScI)

[Koji's blog] Post-apocalyptic Musings

Congratulations! You have survived the end of the world on December 21st, 2012. Many of you who never believed it may nevertheless be relieved, thinking that we can now forget about these apocalyptic prophecies. But, you would be wrong, in my opinion. It’s likely that, before too long, the Internet will be abuzz with new or recycled prophecies of doom. In fact, I don’t think these doomsday predictions are newsworthy, and should largely be ignored, because the end of the world happens so frequently. It does, that is, if you believe everything you read online. There is even a handy list on Wikipedia.

Maybe many rational people enjoy these fantastic scares, the same way many people enjoy horror movies, simply as escapist fun. I, too, enjoyed reading about Nostradamus’s supposed predictions as a young boy. Then there are people who are trying to make money – well, it’s a free country. For example, I don’t resent Hollywood for making the movie 2012, although I think there is much to criticize in a viral ad campaign for that movie. For this, the studio created a non-profit sounding website while effectively hiding any affiliation with the movie. I pity the people who thought that website was for real.

Anyway, I thought this might be a good time to make a few general points related to some of these doomsday scenarios, now that one specific, well-publicized end-of-the-world prediction is behind us.

(1) Do we live in a dangerous universe?

Yes, definitely. But nothing has destroyed the Earth for over 4 billion years, and it’s been about 65 million years since the global extinction that killed off the dinosaurs. Many of the things that disaster prophecies mention – alignments of planets, for example – happen far more frequently than that, without any ill effects. If the human civilization can prosper for millions of years, then we may have to worry about space-based threats to the very existence of our race; over much shorter time frame (centuries, or even millennia), the chances of such huge catastrophes are almost negligible.

Toutatis is an asteroid with an orbit that puts it close enough to Earth to be considered a potentially hazardous object. Scientists believe it poses no real threat, and on December 12, 2012 it passed within 18 lunar distances to Earth.
Credit: NASA’s Deep Space Network antenna in Goldstone

We should, nevertheless, worry about lesser but significant dangers from space – say the equivalent of magnitude 9 earthquakes or category 5 hurricanes. Specifically, we need to worry the most about impacts by comets or asteroids, given what we know of various cosmic dangers. For the last 15 years or so, we have made significant investments of resources to try to discover as many potentially hazardous objects in the Solar system, and none that poses an immediate danger has been found. Smaller objects are harder to discover, and they are more commonplace. One could still strike us with little warning, and cause huge (but far from civilization ending) damage. Our ability to spot potential dangers is improving, people have thought about how one might deal with such objects if found, and we should continue to invest in these areas. Rest assured, also, that scientists are happy and eager to study any other potential dangers out there.

Meteor Crater
Meteor Crater, Arizona. Credit: Maggie Masetti

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[Koji's blog] What is a Galaxy?

“Galaxy,” Defined — when I came across a paper with this title while browsing a recent issue of Astronomical Journal, I was intrigued. You would think that such a widely known term, one so fundamental to modern astronomy, would have been defined a long time ago. But then, sometimes the most widely used words are the very ones that have survived without a formal definition.

More than 200 years ago, Charles Messier compiled his famous catalog to aid him in his quest to discover comets. You see, what he found there were about 100 objects that looked fuzzy, like comets, but didn’t move from night to night. Over the next century or so, astronomers gradually realized that several distinct types of objects were included in the Messier catalog. Some are nebulae, a terminology we reserve today for clouds of gas and dust that shine for one reason or another. Some are star clusters – the Pleiades, for example, is an open cluster with over 1,000 confirmed member stars that are all relatively young. Messier 15, or M15, is a globular cluster, with probably more than 1 million stars.

Hubble image of the Pleiades, credit: NASA, ESA and AURA/Caltech

Then there are what were once called “spiral nebulae.” like the Andromeda galaxy (M31). Back around 1920, some astronomers thought that every star, nebula, and cluster belonged to one system, the Milky Way galaxy. Others thought that the spiral nebulae are island universes of their own. Soon, Hubble observed Cepheid variables in M31 and showed that it was clearly outside the Milky Way. Eventually, we came to call these “galaxies.” If there were only major galaxies with spiral arms, like Andromeda and the Milky Way, then a formal definition might not be necessary – you know a galaxy when you see one.

Andromeda Galaxy
M31, credit: Adam Evans

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[Koji's blog] A Midsummer Day’s Rant

This year, the summer solstice happens on Wednesday, June 20th, in mainland US, at 7:09 pm Eastern Daylight Time. This is often reported in the news as the beginning of the “official” or “astronomical” summer.

Who decided that seasons begin at equinoxes and solstices, though? Words like “equinox” and “solstices” are technical enough that it makes sense for astronomers to define. For example, the June solstice occurs when the Sun is at its northernmost point as seen from the Earth, whose axis of rotation is tilted by 23.5 degrees. But astronomers don’t have the authority (or the audacity) to define common words like spring and summer.

This reminds me of the controversy about the “demotion” of Pluto, when the International Astronomical Union (IAU) change the classification of Pluto from a “planet” to a “dwarf planet.” In my opinion, it’s the IAU’s prerogative to define the word “planet” as used in research papers and astronomy textbooks. I wouldn’t have a problem, though, if Pluto continues to be called a planet in colloquial English. Think of tomatoes – biologically speaking, a tomato is a fruit, but in common usage, it’s a vegetable, and the US Supreme Court agreed!

Credit: Koji Mukai

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[Koji's blog] An “X-ray Astronomer” Among Radio Telescopes

To me, an observational astronomer, there is no such thing as X-ray astronomy. What I do is astronomical research on objects that happen to emit X-rays, as well as ultraviolet, visible, and infrared, etc. light. My research interest is not X-rays, but astronomical objects called cataclysmic variables and symbiotic stars – both involve dense “ash” of sun-like stars called white dwarfs in binary systems.

Having said that, to instrument builders, X-ray astronomy *is* a distinct discipline. Also, it takes time to become adept at using any complex tools and X-ray data analysis is no exception. In that sense, in terms of technical proficiency, I am an X-ray astronomer. I have also worked with infrared, visible light, and ultraviolet observations before – but not radio observations, not even by collaborating with the experts, until recently.

This is changing, partly because a phenomenon I’m very interested in called “nova outburst” can produce radio waves and X-ray photons. Basically, novae are nuclear explosions on the surface of the white dwarfs in cataclysmic variables and symbiotic stars. The material ejected (called ejecta) from these explosions emit radio waves when they are just expanding. However, collisions within the ejecta or collisions of the ejecta with some other materials can heat them up to many millions of degrees, making them bright in X-rays. So it makes a lot of sense to observe novae with X-rays and radio at the same time. Another reason for my evolving collaboration is that the premier instrument of radio astronomy has undergone a significant upgrade in the last several years, making them capable of doing observations that were never possible before.

Recently, I had the chance to visit the Science Operations Center of National Radio Astronomy Observatory (NRAO) in Socorro, New Mexico. About one hour west, on the high plains of San Augustin, is what used to be called the Very Large Array (VLA). The VLA uses a set of 27 antennas, each having a diameter of 25 meters (or 82 feet). By combining the signals from these antennas, the VLA acts like a much bigger telescope – the separations of the antennas, not the size of each individual antenna, determine how detailed an image we get (“the angular resolution”). The antennas of the VLA can be moved along special railroad tracks to several pre-constructed stations to suit the need of the observers. It’s a stunning sight to see the VLA, particularly when the entire array is moving from one target on the sky to the next. I even got to climb up on the 28th antenna undergoing routine maintenance (you don’t want to do that with ones in use – for one thing, if the antenna is tilted to observe an object low in the sky, it would be very dangerous).

Credit: Koji Mukai

Credit: Koji Mukai

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[Koji's blog] Archiving the Past for the Future

There is a group here at Goddard is called the HEASARC – High Energy Astrophysics Science Archive Research Center. This is where we keep data from old and new satellites. Even though every new satellite is an improvement over the last in one way or another, it is important to keep old data, with the expertise to go with it.

Think of Halley’s Comet – when Edmund Halley calculated the orbit of this comet from observations in 1682, he was able show that it was the same as the comets of 1531 and 1607 because there were sufficiently detailed records from those appearances.

Halley's Comet
Halley’s Comet. Credit: NASA

We now know of even earlier appearances of Halley’s Comet, dating back at least to the Chinese record of of a comet in 240 BC. Chinese court astrologers had a habit of making careful records of not only comets but novae and supernovae, which they collectively called “guest stars.” These records are invaluable to today’s astrophysicists who also use modern telescopes and satellites. For example, historical records can give you the precise age of a supernova since the explosion.

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[Koji's Blog] Paying Tribute to the Scientists of the 16th & 17th Centuries

We all know that Nicolaus Copernicus revolutionized our view of the universe. Who would you pick as the top scientists who further developed astronomy during the 16th and 17th centuries? I would pick Tycho Brahe, Johannes Kepler, Galileo Galilei, Isaac Newton, and Edmond Halley as my top five. I got to think about these giants of the field during my recent European trip, as I had the chance to see sights connected directly to three of these five, and indirectly to a fourth.

Halley’s major contribution was that he calculated the orbit of the comet that now bears his name – he applied his friend Newton’s laws of physics, and realized that the comet of 1682 had previously been seen in 1531 and in 1607, and predicted, correctly, its return in 1758. In this, he went beyond Newton and included the approximate effect of the gravity of Jupiter.

During its return in 1986, several spacecraft visited Halley’s comet, including European Space Agency’s Giotto mission. When a space probe is named after a person, that person usually is a famous scientist. In this case, though, ESA picked Giotto, who was an architect and a painter, and I got to see one of his masterpieces, the Scrovegni Chapel in Padua (Padova), Italy. Giotto painted many religious scenes in the year 1305 or so in the interior of this chapel. In one of them, the Adoration of the Magi, he incorporated his interpretation of the star of Bethlehem – a comet. This is widely thought to have been inspired by the sight of Halley’s comet from its appearance in 1301, 5 orbits before Halley saw it, and 9 orbits before Giotto the spacecraft would visit it.

Adoration of the Magi, by Giotto
Adoration of the Magi, by Giotto

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[Koji's blog] Astronomical Eye Candy

The HEASARC Picture of the Week for the week for Mar 21 is titled “The Ring.” Maggie posted the same image on Blueshift on Valentine’s Day, with a caption based on a Chandra press release. It sure is a pretty picture, combining Hubble and Chandra data, with a romantic connotation.

Giant Ring of Black Holes
Credit: X-ray: NASA/CXC/MIT/S.Rappaport et al, Optical: NASA/STScI

This got me thinking about the overwhelming abundance of pretty pictures among astronomical press releases. Because, to be honest, Chandra released this image to the press a few days before Valentine’s purely because it’s pretty and Valentine-ish, not because of its scientific significance.

Don’t get me wrong. I have no intention of denigrating the science behind this image. However, the paper containing this image was published in the October 1, 2010 issue of the Astrophysical Journal. You don’t issue a press release about a scientific discovery, over 4 months after the paper was published. It was a pure case of seasonal eye candy.

There is nothing wrong with eye candy – well, at least not with the astronomical kind. But it makes me sad if that’s all astronomy is, a source of pretty images, to the general public. More than that, I think it can be damaging to the field of astronomy.

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[Koji's blog] Even Spherical Cows Have Udders

In astrophysics, we often use the term “standard candle.” It is a highly useful, yet also very dangerous, term.

The danger is that outsiders – the press, the general public, and even some scientists who are not intimately familiar with this particular subject – see this term and take it too literally. As an analogy, take the spherical cow, which has become a symbol of simplifying assumptions. Such assumptions make back-of-the envelope calculations possible. But a “spherical” cow is an approximation – if someone forgets this and says “since cows are spherical, they can’t have features like udders,” you would laugh him off. In less extreme and more common cases, people may forget to check the difference between the volume of a spherical cow and that of actual cows with a head, a tail, four legs, and udders. Some other people may ignore the fact that the volume of a real cow is not a unique function of its height. I have noticed a similar type of sloppiness regarding “standard” candles.

A cow [15/365]
Image Credit: Dave Wild (publicenergy)

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