Astronomers find colossal ring system putting Saturn’s to shame

An astronomy professor at the University of Leiden, Ignas Snellen,called brown dwarfs ‘failed stars‘ because they were too heavy to be typical planets (13-75 times as heavy as Jupiter) and too light to sustain the fusion of hydrogen into helium. As a result, they exist in a limbo in astronomers’ textbooks, with the precise mechanism of their formation remaining a mystery.

However, failed or no, brown dwarfs are still massive objects and make for interesting features in the universe. One stellar example is the pithily named J1407b. It was discovered in 2012 by astronomers at the Leiden Observatory and University of Rochester, New York, orbiting a star – J1407 – about 420 light-years from Earth. J1407b is young – about 16 million years old. But it’s most striking feature is an extended ring system.

In 2012, the astronomers studying it surmised that the dwarf likely has 37 rings, altogether 120 million km in diameter (as wide as Mercury’s orbit around the Sun). Compare this to Saturn’s ring system, which is at most 300,000 km wide*. There are conspicuous gaps between these rings as well – notably at a distance of about 60 million km from the inside – indicating that there might be moons inhabiting them, formed by sweeping up the missing material.

Artist’s conception of the extrasolar ring system circling the young giant planet or brown dwarf J1407b. The rings are shown eclipsing the young sun-like star J1407, as they would have appeared in early 2007.
Artist’s conception of the extrasolar ring system circling the young giant planet or brown dwarf J1407b. The rings are shown eclipsing the young sun-like star J1407, as they would have appeared in early 2007. Credit: Ron Miller

The research team estimates that the amount of material orbiting as rings might all together weigh as much as hundred-times Earth’s moon, which is not anomalous considering J1407b is still young and likely not fully formed yet.

The way it was discovered is interesting. An exoplanet shows itself when seen through a telescope when it passes in front of its host star and casts a weak but persistent shadow on the telescope lens. When observing the J1407 system using the Super Wide Angle Search for Planets project in 2007, the astronomers found something was taking 56 days to move all the way across the face of its star. It was either an extremely large object or it had rings.

Model ring fit to J1407 data.
Model ring fit to J1407 data. The red data-points at the bottom show the dips in starlight intensity. The curve fitting them is plotted in green. Credit: Kenworthy, MA & Mamajek, EE. arXiv

A second observation supported the rings hypothesis: the amount of starlight blocked wasn’t constant, but rose and dipped as if the amount of material passing in front of it was uneven. In fact, at one point, fully 95% of the starlight was blocked.

“The star is much too far away to observe the rings directly, but we could make a detailed model based on the rapid brightness variations in the star light passing through the ring system,” noted Leiden’s Matthew Kenworthy, who analyzed the data. “If we could replace Saturn’s rings with the rings around J1407b, they would be easily visible at night and be many times larger than the full moon.”

Estimating the mass of the ring-system would’ve required Doppler spectroscopy data as well, which wasn’t available until late 2014.

Curiously, the planet J1407b hasn’t been spotted directly yet. The astronomers are assuming it’s there simply because something like it has to hold this ring system together. In fact, its characterization as a brown dwarf is simply what it has to be at the least. The Doppler data indicates it has to weight some 10-40 times as much as Jupiter, i.e. much bigger than a gas giant, much smaller than a main-sequence star.

A paper discussing the team’s results was accepted for publication in the Astrophysical Journal on December 28, 2014. Even as studies of this giant will continue, the astronomers have called on their amateur counterparts from around the world to help them. “J1407’s eclipses will allow us to study the physical and chemical properties of satellite-spawning circumplanetary disks,” Kenworthy said of incentives.

*Not counting the feeble Phoebe ring.

Astronomers find colossal ring system dwarfing Saturn’s

An astronomy professor at the University of Leiden, Ignas Snellen,called brown dwarfs ‘failed stars‘ because they were too heavy to be typical planets (13-75 times as heavy as Jupiter) and too light to sustain the fusion of hydrogen into helium. As a result, they exist in a limbo in astronomers’ textbooks, with the precise mechanism of their formation remaining a mystery.

However, failed or no, brown dwarfs are still massive objects and make for interesting features in the universe. One stellar example is the pithily named J1407b. It was discovered in 2012 by astronomers at the Leiden Observatory and University of Rochester, New York, orbiting a star – J1407 – about 420 light-years from Earth. J1407b is young – about 16 million years old. But it’s most striking feature is an extended ring system.

In 2012, the astronomers studying it surmised that the dwarf likely has 37 rings, altogether 120 million km in diameter (as wide as Mercury’s orbit around the Sun). Compare this to Saturn’s ring system, which is at most 300,000 km wide*. There are conspicuous gaps between these rings as well – notably at a distance of about 60 million km from the inside – indicating that there might be moons inhabiting them, formed by sweeping up the missing material.

Artist’s conception of the extrasolar ring system circling the young giant planet or brown dwarf J1407b. The rings are shown eclipsing the young sun-like star J1407, as they would have appeared in early 2007.
Artist’s conception of the extrasolar ring system circling the young giant planet or brown dwarf J1407b. The rings are shown eclipsing the young sun-like star J1407, as they would have appeared in early 2007. Credit: Ron Miller

The research team estimates that the amount of material orbiting as rings might all together weigh as much as hundred-times Earth’s moon, which is not anomalous considering J1407b is still young and likely not fully formed yet.

The way it was discovered is interesting. An exoplanet shows itself when seen through a telescope when it passes in front of its host star and casts a weak but persistent shadow on the telescope lens. When observing the J1407 system using the Super Wide Angle Search for Planets project in 2007, the astronomers found something was taking 56 days to move all the way across the face of its star. It was either an extremely large object or it had rings.

Model ring fit to J1407 data.
Model ring fit to J1407 data. The red data-points at the bottom show the dips in starlight intensity. The curve fitting them is plotted in green. Credit: Kenworthy, MA & Mamajek, EE. arXiv

A second observation supported the rings hypothesis: the amount of starlight blocked wasn’t constant, but rose and dipped as if the amount of material passing in front of it was uneven. In fact, at one point, fully 95% of the starlight was blocked.

“The star is much too far away to observe the rings directly, but we could make a detailed model based on the rapid brightness variations in the star light passing through the ring system,” noted Leiden’s Matthew Kenworthy, who analyzed the data. “If we could replace Saturn’s rings with the rings around J1407b, they would be easily visible at night and be many times larger than the full moon.”

Estimating the mass of the ring-system would’ve required Doppler spectroscopy data as well, which wasn’t available until late 2014.

Curiously, the planet J1407b hasn’t been spotted directly yet. The astronomers are assuming it’s there simply because something like it has to hold this ring system together. In fact, its characterization as a brown dwarf is simply what it has to be at the least. The Doppler data indicates it has to weight some 10-40 times as much as Jupiter, i.e. much bigger than a gas giant, much smaller than a main-sequence star.

A paper discussing the team’s results was accepted for publication in the Astrophysical Journal on December 28, 2014. Even as studies of this giant will continue, the astronomers have called on their amateur counterparts from around the world to help them. “J1407’s eclipses will allow us to study the physical and chemical properties of satellite-spawning circumplanetary disks,” Kenworthy said of incentives.

*Not counting the feeble Phoebe ring.

Rosetta’s comet sheds its coat for warmer times

This animation comprises 24 montages based on images acquired by the navigation camera on the European Space Agency's Rosetta spacecraft orbiting Comet 67P/Churyumov-Gerasimenko between Nov. 19 and Dec. 3, 2014.
This animation comprises 24 montages based on images acquired by the navigation camera on the European Space Agency’s Rosetta spacecraft orbiting Comet 67P/Churyumov-Gerasimenko between Nov. 19 and Dec. 3, 2014. Credit: ESA/Rosetta/NAVCAM

Fascinating things are happening to the world’s most-watched comet, 67P/Churyumov-Gerasimenko, as it approaches the Sun. A new study from NASA and ESA scientists published in Nature reports that by January 20, 67P shed a crust of dust built up on its surface over the last four years. In fact, by the end of January – about a week from now – the study’s authors expect heat and other radiation from the Sun will strip off the comet’s crust and mantle, exposing the icy nucleus.

As the comet hurtles into increasingly warmer space, the nucleus will start to evaporate into a dull haze around it that progressively forms the iconic tail as the ambient temperature increases. On August 13, 2015, 67P is expected to achieve perihelion, its closest distance from the Sun, at 185.98 million km.

The expelled dust was collected and analyzed by the ESA Rosetta probe that is tracking the comet, specifically by its Cometary Secondary Ion Mass Analyzer. It was found to be porous and rich in sodium, indicating that it may be the origin of particulate grains often found floating in the space between planets in the Solar System. The dust’s composition also challenges older notions that such grains are dominated by silicates.

Losing the dust

The deceptively simple process of shedding dust tells astronomers a lot about the comet’s composition and how it will change over time. The comet needs to be at a particular distance from a star for stellar radiation to whip away the dust from the surface. Therefore, based on the comet’s route from the Oort Cloud and toward the center of the Solar System, astronomers can deduce under what conditions the dust was accumulated to begin with.

As the dust builds up on the surface, it forms more and more layers devoid of icy particles borrowed from the comet’s nucleus. And as the whole comet heats up, the layers at the bottom start to vaporize first and unsettle the dust from the upper layers into a haze, called the coma, around it. Moreover, dust from the lower layers also starts getting floated toward the surface as a result of the icy grains started to melt. The overall effect – as the comet approaches the Sun – is for the coma to grow larger even as dust from the lower layers replenishes the coating on the surface.

At one point, however, the strength of the Sun’s radiation becomes strong enough to expel dust faster than it can be replenished – which is what is happening to 67P at the moment (Curiously, data from various instruments shows that the ‘neck’ region of this duck-shaped comet is losing dust the fastest).

The transition from when the replenishing mechanism is active to when dust is only getting expelled is usually smooth. Sometimes, however, it can be violent if there is a hard, intervening layer between the dust and the nucleus. Such a layer could be present on 67P, too, as evinced by the fact that the Rosetta probe’s lander Philae bounced around a bit on the comet’s surface on November 12, 2014, before it could latch itself on.

Other gases

In all this time, two other instruments on board Rosetta, the Microwave Instrument for Rosetta Orbiter and Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, have also been studying how the rates at which the cometary water vapor and other gases – such as carbon dioxide and carbon monoxide – being released from the nucleus vary. They have together found that while water vapor dominates the contents of the expelled matter, there are occasional spikes in the quantity of the two gases, too.

Myrtha Hässig, a NASA-sponsored scientist from the Southwest Research Institute, San Antonio, said, “This variation could be a temperature effect or a seasonal effect, or it could point to the possibility of comet migrations in the early solar system.”

Such conclusions, from the characteristics of dust erosion on the surface to its possible internal composition, as well as the more speculative ideas of cometary migration concern not just 67P but the broader class of short-period comets, many of which visit the Sun at least once every 200 years. Astronomers think their long journeys makes them well-suited to be messengers carrying non-native molecules to worlds that might not have otherwise acquired them – such as those necessary for life on Earth.

Rosetta's comet sheds its coat for warmer times

This animation comprises 24 montages based on images acquired by the navigation camera on the European Space Agency's Rosetta spacecraft orbiting Comet 67P/Churyumov-Gerasimenko between Nov. 19 and Dec. 3, 2014.
This animation comprises 24 montages based on images acquired by the navigation camera on the European Space Agency’s Rosetta spacecraft orbiting Comet 67P/Churyumov-Gerasimenko between Nov. 19 and Dec. 3, 2014. Credit: ESA/Rosetta/NAVCAM

Fascinating things are happening to the world’s most-watched comet, 67P/Churyumov-Gerasimenko, as it approaches the Sun. A new study from NASA and ESA scientists published in Nature reports that by January 20, 67P shed a crust of dust built up on its surface over the last four years. In fact, by the end of January – about a week from now – the study’s authors expect heat and other radiation from the Sun will strip off the comet’s crust and mantle, exposing the icy nucleus.

As the comet hurtles into increasingly warmer space, the nucleus will start to evaporate into a dull haze around it that progressively forms the iconic tail as the ambient temperature increases. On August 13, 2015, 67P is expected to achieve perihelion, its closest distance from the Sun, at 185.98 million km.

The expelled dust was collected and analyzed by the ESA Rosetta probe that is tracking the comet, specifically by its Cometary Secondary Ion Mass Analyzer. It was found to be porous and rich in sodium, indicating that it may be the origin of particulate grains often found floating in the space between planets in the Solar System. The dust’s composition also challenges older notions that such grains are dominated by silicates.

Losing the dust

The deceptively simple process of shedding dust tells astronomers a lot about the comet’s composition and how it will change over time. The comet needs to be at a particular distance from a star for stellar radiation to whip away the dust from the surface. Therefore, based on the comet’s route from the Oort Cloud and toward the center of the Solar System, astronomers can deduce under what conditions the dust was accumulated to begin with.

As the dust builds up on the surface, it forms more and more layers devoid of icy particles borrowed from the comet’s nucleus. And as the whole comet heats up, the layers at the bottom start to vaporize first and unsettle the dust from the upper layers into a haze, called the coma, around it. Moreover, dust from the lower layers also starts getting floated toward the surface as a result of the icy grains started to melt. The overall effect – as the comet approaches the Sun – is for the coma to grow larger even as dust from the lower layers replenishes the coating on the surface.

At one point, however, the strength of the Sun’s radiation becomes strong enough to expel dust faster than it can be replenished – which is what is happening to 67P at the moment (Curiously, data from various instruments shows that the ‘neck’ region of this duck-shaped comet is losing dust the fastest).

The transition from when the replenishing mechanism is active to when dust is only getting expelled is usually smooth. Sometimes, however, it can be violent if there is a hard, intervening layer between the dust and the nucleus. Such a layer could be present on 67P, too, as evinced by the fact that the Rosetta probe’s lander Philae bounced around a bit on the comet’s surface on November 12, 2014, before it could latch itself on.

Other gases

In all this time, two other instruments on board Rosetta, the Microwave Instrument for Rosetta Orbiter and Rosetta Orbiter Spectrometer for Ion and Neutral Analysis, have also been studying how the rates at which the cometary water vapor and other gases – such as carbon dioxide and carbon monoxide – being released from the nucleus vary. They have together found that while water vapor dominates the contents of the expelled matter, there are occasional spikes in the quantity of the two gases, too.

Myrtha Hässig, a NASA-sponsored scientist from the Southwest Research Institute, San Antonio, said, “This variation could be a temperature effect or a seasonal effect, or it could point to the possibility of comet migrations in the early solar system.”

Such conclusions, from the characteristics of dust erosion on the surface to its possible internal composition, as well as the more speculative ideas of cometary migration concern not just 67P but the broader class of short-period comets, many of which visit the Sun at least once every 200 years. Astronomers think their long journeys makes them well-suited to be messengers carrying non-native molecules to worlds that might not have otherwise acquired them – such as those necessary for life on Earth.

Why does sodium react so explosively with water?

In January 1947, the American War Assets Administration dumped drums of sodium left over after the end of World War II into Lake Lenore in eastern Washington state. A video of the event – it really was an event – is available from the Internet Archive.

Sodium’s reaction with water – or most other substances in general – is so violent because of the number of electrons in its atoms. Specifically, each sodium atom has one electron more than the atom needs to be in a highly stable state. That one electron keeps the atom highly unstable, and is given away at the first available chemical opportunity. So, when sodium (Na) meets water (HO–H), it rapidly forms sodium hydroxide (Na–OH) and releases hydrogen (H). Simultaneously, the sodium atoms release their extra electrons to form the molecules, and from go being highly unstable to highly stable. As a result, they produce such heat that the hydrogen is ignited, which burns with a bright flame, even as some of the water boils off as steam.

Even if all of this makes sense – and is true – could there be more to this reaction than meets the eye?

That’s the question a bunch of chemists, from the Academy of Sciences of the Czech Republic and the Technical University of Braunschweig, Germany, chose to ask. They figured the explosive nature of the reaction wasn’t solely due to sodium’s eagerness to react with water but also had to do with how its surface changed shape when in contact with water. Using high-speed cameras, they studied how drops of an alloy of sodium and potassium, another explosively reactive metal, responded when they were dropped into water. Watch this closely.

Credit: Mason et al.

Toward the end of the video (as Thunderf00t explains in the 17th minute), you can see how almost as soon as it is dropped, the alloy rapidly develops spike-like protrusions on its surface, on the underside. These spikes form within a few thousandths of a second, and increase the surface area of the metal that is available to react with water. The scientists calculated based on their video footage that the spikes start and finish extending out of the surface at an acceleration of 10,000 ms-2. That’s almost the same acceleration at which you could be shot out of a space gun.

Caption: First experiments of the alkali metal explosion in water performed at the balcony of the Institute in Prague provided important clues for later more rigorous laboratory studies (and lots of fun).
First experiments of the alkali metal explosion in water performed at the balcony of the Institute in Prague provided important clues for later more rigorous laboratory studies (and lots of fun). Credit: Phil Mason

When they performed the same experiment with a drop of liquid aluminium, they couldn’t see any spikes forming on the metal droplet. Apparently, it happened only with the sodium-potassium alloy. Was it because of the explosion that happens? Nope, because sodium-potassium reacts non-explosively with ammonia, but the spikes formed there again. So it definitely happens only with sodium-potassium.

So, to get their answer, the scientists used a computer simulation, which revealed an all too familiar devil in the details.

As soon as the sodium-potassium drop meets with the surface of water, its outermost layer of atoms loses electrons rapidly to the water – so fast that the transfer happens in a few trillionths of a second. The water molecules accept the electrons and subsequently break down into hydroxyl (HO) and hydrogen (H) ions. As a result, at the interface of the drop and the water, there are now four layers: the remaining drop of sodium-potassium atoms, next a layer of sodium-potassium ions (positively charged because they’ve lost electrons), then a layer of hydrogen and hydroxyl ions (positively and negatively charged, respectively), and finally the rest of the water.

ions

As you can see, there is a layer of positively charged sodium and potassium ions, and like charges repel each other. Because the sodium-potassium alloy is in liquid form, the repulsion manifests as highly distended droplets, or spikes. In technical parlance, this phenomenon is called coulomb fission. The resultant increase in surface area prevents the reaction from stalling, which might have happened if the first layer of sodium hydroxide to form was let to act like a blanket protecting the rest of the alloy.

The English physicist John William Strutt (better known as Lord Rayleigh) first predicted this for liquids in 1882. He reasoned that an electrically charged drop could only contain so much charge before its surface tension gave way and let the drop break up into droplets by ejecting jets – called Rayleigh jets – out of their sides. The Czech and German scientists used high-school math to figure that this breakdown happens as soon as the distance between the sodium-potassium ions and the electrons and hydroxyl ions becomes more than 5 angstrom (one angstrom is a ten-billionth of a meter).

So, that’s one high-school chemistry lesson fully unraveled. How about going after the vinegar volcano next?

The scientists’ paper was published in Nature Chemistry on January 26 .

Caution: This piece contains a lot of mentions of the word ‘jargon’.

Credit: The Sales Whisperer/Flickr.
Credit: The Sales Whisperer/Flickr

When writing one of my first pieces for The Hindu, I remember being called out for using a lot of jargon. While the accusation itself may have been justified, the word my supervisor chose as an example of the problem was surprising: “refraction”. He wanted me to spell it out in 10 words or so (because we were already running out of print-space). When I couldn’t, he launched into a long tirade.

It’s easy to spell out the what of refraction in 10 words – just refer to a prism. But if you’ve to understand the why, you’ll end up somewhere in the vicinity of quantum mechanics. At the same time, there are some everyday concepts in our lives that are easier understood the way they appear to be than in terms of what they actually are. This is where I’d draw the line of jargon. While everything can be technically simplified to the predictions of a complicated theory like quantum mechanics, jargon is that which isn’t at its simplest in the most pragmatic sense.

Clearly, this line lies in different places for different people because it can be moved by specialized knowledge. Writing in Nature or Science, I can take for granted that my audience will understand concepts like resonance or Feynman diagrams. Writing in The Hindu, on the other hand, all I can take for granted is reflection and, hopefully, refraction. Then again, these are publications who (ought to) know what their target audience is like. So I ask: If you were writing for a billion people, where would you assume the line is?

To me, the line would be at the statistical mode.

What irks me is that – in India at least – the statistical mode for different topics lies at incomparably different places. For example, I would be able to get away with ‘repo rate’ and ‘tortfeasor’ but not ‘morbidity’. My first impression was to somehow peg the difference to the well-established lack of scientific temper. But then I realized what the bigger problem was: news publications in the country are in a state of denial about lacking the scientific temper themselves, and consistently refuse to subject financial and legal news to the same scrutiny and the same wariness with which science news is treated.

If editors really wanted to take responsibility for their content, they wouldn’t let repo rate go through the press, or tortfeasor, or short fine leg, or Brent crude, or fiscal deficit*, or the history of the BJP**. However, they have let these bits of information go through without any apprehensions that they might be misunderstood or not understood at all. And by doing so, they have engendered an invisible reading culture that enforces the notion that these words don’t require further explanation, that these words shouldn’t be jargon – rather, wouldn’t be jargon if not for the reader’s ignorance.

In this culture, business and politics news (henceforth: fin-pol) can be for the least common denominators among all readers while science news… well, science news isn’t for everyone, is it? While the editors have misguidedly but efficiently dejargonized fin-pol news, with the effect that while fin-pol content is considered conventional, science news is still asked to be delivered sandwiched between layers of didactic material.

Another problem – this one more subtle and less prevalent – is that fin-pol reporters can often bank on historical knowledge while science reporters, word for word, remain constrained by the need to break down jargon. In other words, the fin-pol writer can assume the reader knows what he/she is talking about but ‘Feynman diagrams’ have to be repeatedly laid out unless the article is explicitly specified as being one in a series.

*If I can’t use ‘refraction’, you can’t use ‘fiscal deficit’.
**If you refuse to learn from sources other than the media as to who MSR Dev is, I refuse to let myself be persecuted for not learning from sources other than the media as to who SP Mukherjee was.

Caution: This piece contains a lot of mentions of the word 'jargon'.

Credit: The Sales Whisperer/Flickr.
Credit: The Sales Whisperer/Flickr

When writing one of my first pieces for The Hindu, I remember being called out for using a lot of jargon. While the accusation itself may have been justified, the word my supervisor chose as an example of the problem was surprising: “refraction”. He wanted me to spell it out in 10 words or so (because we were already running out of print-space). When I couldn’t, he launched into a long tirade.

It’s easy to spell out the what of refraction in 10 words – just refer to a prism. But if you’ve to understand the why, you’ll end up somewhere in the vicinity of quantum mechanics. At the same time, there are some everyday concepts in our lives that are easier understood the way they appear to be than in terms of what they actually are. This is where I’d draw the line of jargon. While everything can be technically simplified to the predictions of a complicated theory like quantum mechanics, jargon is that which isn’t at its simplest in the most pragmatic sense.

Clearly, this line lies in different places for different people because it can be moved by specialized knowledge. Writing in Nature or Science, I can take for granted that my audience will understand concepts like resonance or Feynman diagrams. Writing in The Hindu, on the other hand, all I can take for granted is reflection and, hopefully, refraction. Then again, these are publications who (ought to) know what their target audience is like. So I ask: If you were writing for a billion people, where would you assume the line is?

To me, the line would be at the statistical mode.

What irks me is that – in India at least – the statistical mode for different topics lies at incomparably different places. For example, I would be able to get away with ‘repo rate’ and ‘tortfeasor’ but not ‘morbidity’. My first impression was to somehow peg the difference to the well-established lack of scientific temper. But then I realized what the bigger problem was: news publications in the country are in a state of denial about lacking the scientific temper themselves, and consistently refuse to subject financial and legal news to the same scrutiny and the same wariness with which science news is treated.

If editors really wanted to take responsibility for their content, they wouldn’t let repo rate go through the press, or tortfeasor, or short fine leg, or Brent crude, or fiscal deficit*, or the history of the BJP**. However, they have let these bits of information go through without any apprehensions that they might be misunderstood or not understood at all. And by doing so, they have engendered an invisible reading culture that enforces the notion that these words don’t require further explanation, that these words shouldn’t be jargon – rather, wouldn’t be jargon if not for the reader’s ignorance.

In this culture, business and politics news (henceforth: fin-pol) can be for the least common denominators among all readers while science news… well, science news isn’t for everyone, is it? While the editors have misguidedly but efficiently dejargonized fin-pol news, with the effect that while fin-pol content is considered conventional, science news is still asked to be delivered sandwiched between layers of didactic material.

Another problem – this one more subtle and less prevalent – is that fin-pol reporters can often bank on historical knowledge while science reporters, word for word, remain constrained by the need to break down jargon. In other words, the fin-pol writer can assume the reader knows what he/she is talking about but ‘Feynman diagrams’ have to be repeatedly laid out unless the article is explicitly specified as being one in a series.

*If I can’t use ‘refraction’, you can’t use ‘fiscal deficit’.
**If you refuse to learn from sources other than the media as to who MSR Dev is, I refuse to let myself be persecuted for not learning from sources other than the media as to who SP Mukherjee was.

HESS telescopes discover new source of gamma rays called a superbubble

Optical image of the Milky Way and a multi-wavelength (optical, Hα) zoom into the Large Magellanic Cloud with superimposed H.E.S.S. sky maps.
Optical image of the Milky Way and a multi-wavelength (optical, Hα) zoom into the Large Magellanic Cloud with superimposed H.E.S.S. sky maps. (Milky Way image: © H.E.S.S. Collaboration, optical: SkyView, A. Mellinger; LMC image: © H.E.S.S. Collaboration, Hα: R. Kennicutt, J.E. Gaustad et al. (2001), optical (B-band): G. Bothun

Astronomers using the HESS telescopes have discovered a new source of high-energy gamma rays. Dubbed a superbubble, it appears to be a massive shell of gas and dust 270 light-years in diameter being blown outward by the radiation from multiple stars and supernovas. HESS also discovered two other gamma-ray sources, each a giant of its kind. One is a powerful supernova remnant and the other a pulsar wind nebula. All three objects are located in the Large Magellanic Cloud, a small satellite galaxy orbiting the Milky Way at a distance of 170,000 ly. As a result, these objects are not only the most luminous gamma-ray sources discovered to date but also the first sources discovered outside the Milky Way.

Gamma-rays are emitted when very energetic charged particles collide with other particles, such as in a cloud of gas. Therefore, gamma radiation in the sky is often used as a proxy for high-energy phenomena. And astronomers have for long known that the Large Magellanic Cloud houses many such clusters of frenzied activity: weight for weight of their stars, the Cloud’s supernova rate is five times that of the Milky Way. It also hosts the Tarantula Nebula, which is the most active star-forming region in the Local Group of galaxies (which includes the Milky Way, Andromeda, the Cloud and more than 50 others).

Super-luminous sources

It is in this environment that the superbubble – designated 30 Dor C – thrives. According to the HESS team’s notice, it “appears to have been created by several supernovae and strong stellar winds”. In the data, it is visible as a strong source of gamma-rays because it is filled by highly energetic particles. The notice adds that this freak of nature

“represents a new class of sources in the very high-energy regime.”

The other two super-luminous sources are familiar to astronomers. Pulsars, especially, are the extremely dense remnants of stars that have run out of hydrogen to fuse and imploded, resulting in a rapidly spinning core composed of neutrons and wound by fierce magnetic fields. They emit a jet of energetic particles from polar points on their surface that form nebulaic clouds. One such cloud is N 157B, emitted by PSR J0537 – 6910. According to the HESS team, N 157B outshines the Crab Nebula in gamma-rays. The Crab Nebula is Milky Way’s most famous and most powerful source of gamma-rays.

The third is a supernova remnant: the rapidly expanding shell of gas that a once-heavy dying star blows away as its core collapses. The shell can be expelled at more than thousand times the speed of sound, resulting in a shockwave that can accelerate nearby particles and heat up upstream gas clouds to millions of kelvin. The resulting glow can last for thousands of years – but the one HESS has seen in the Cloud seems to going strong for 2,500-6,000 years, much longer than astronomers thought possible. It’s called N132D.

“Obviously, the high star formation rate of the LMC causes it to breed very extreme objects,” said Chia Chun Lu, a student at the Max Planck Institute for Astronomy in Heidelberg who analyzed the data for her thesis.

Imaging Cherenkov radiation

Detecting gamma-rays is no easy task because it requires the imaging of Cherenkov radiation. Just as when a jet flies through air at faster than the speed of sound and results in a sonic boom, a charged particle traveling at faster than the speed of light in that medium results in a shockwave of energy called Cherenkov radiation. This typically lasts a few billionths of a second and requires extremely sensitive cameras to capture.

When high-energy particles collide with the upper strata of Earth’s atmosphere, they percolate through while triggering the release of Cherenkov radiation. The five ground-based HESS telescopes – whose name stands for High Energy Stereoscopic System – quickly capture their bluish flashes before they disappear, and reconstruct their sources’ energy based on theirs. So, while gamma-rays can be a proxy for high-energy phenomena in the distant reaches of the cosmos, Cherenkov radiation in the upper atmosphere is a proxy for the gamma radiation itself.

Very-high-energy gamma-rays, of the order emitted by the Crab pulsar at the center of its nebula, are often the result of events that have made astronomers redefine what they consider anomalous. A good example is of GRB 080916C, a gamma-ray burst spotted in 2009 at about 12 billion ly from Earth. It was the result of a star collapsing into a black hole, with consequent ‘burp’ of energy lasting for a whopping 23 minutes. Valerie Connaughton, of the University of Alabama, Huntsville, and one of the members of the team studying the burst, said of its energy: “… it would be equivalent to 4.9 times the mass of the sun being converted to gamma rays in a matter of minutes”.

Natural particle accelerators

Such profuse emissions can behave like natural particle accelerators, often reaching energies the Large Hadron Collider can only dream of. They give scientists the opportunity to study particles as well as the vacuum of space in conditions closer to that prevalent at the time of the Big Bang, in effect rendering the telescopes that study them as probes of fundamental physics. In the case of GRB 080916C, for example, low-energy gamma-rays dominated the first five seconds of emissions, following by the high-energy gamma-rays for the next twenty minutes. As astronomy-blogger Paul Gilster interpreted this,

They might also give us a read on theories of quantum gravity that suggest empty space is actually a froth of quantum foam, one that would allow lighter, lower-energy gamma rays to move more quickly than their higher-energy cousins. Future observations to study unusual time lags like these should help us pin down a plausible explanation.

The Fermi orbiting telescope that spotted the burst is also used to look for dark matter. When certain hypothetical particles of dark matter annihilate or decay, they yield high-energy antielectrons that could then annihilate upon colliding with electrons and yield gamma-rays. These are measured by Fermi. Then, astronomers use preexisting data as a filter to extrude anomalous observations and use it inform their theories of dark matter.

In this sense, the HESS telescopes are important observers of the universe. They comprise five telescopes, of which four, each 12 meters in diameter, are situated on the corners of a square of side 120 m. At the center is the fifth telescope of diameter 28 m. The array, fixed up with computers to work as one big telescope, is located in Namibia, and is capable of observing gamma-ray fluxes in the range 30 GeV to 100 TeV. In 2015, in fact, construction for the more-impressive $268-million Cherenkov Telescope Array will start. Upon completion, it will be able to study gamma-ray fluxes of 100 TeV but with a wider angle of observation and much larger collecting area.

Whether or not the CTA can pinpoint the existence of dark matter, it will likely allow astronomers to discover more superbubbles, pulsar wind nebulae, supernova remnants and gamma-ray bursts, each more revealing than the last about the universe’s deepest secrets.

‘Nothing in the history of science is ever simple’

Once I finished Steven Weinberg’s book Dreams of a Final Theory, I figured I’d write a long-winding review about what I think the book is really about, and its merits and demerits. But there is a sentence in the seventh chapter – titled ‘Against Philosophy’ – which I think sums up all that the book essentially attempts to explain.

Nothing in the history of science is ever simple.

And Dreams of a Final Theory wants to make you understand why that is so. To Weinberg’s credit, he has done a good job – not a great one – with complexity as his subject. I say ‘not a great one’ because it has none of the elegance that Brian Greene’s The Elegant Universe did, and it laid out string theory from beginning to end. At the same time, it is still Weinberg, one of the towering figures of particle physics, at work, and he means to say, first, that there is no place for simplicity in his line of work and, second, even in all the terrible complexity, there is beauty.

The book, first published in 1992, is a discourse on the path to a ‘final theory’ – one theory to rule them all, so to speak – and the various theoretical, experimental, mathematical and philosophical challenges it presents. Weinberg is an erudite scientist and you can trust him to lay out almost all facets of all problems that he chooses to introduce in the book – and there are many of them. Also, I wouldn’t call the book technical, but at the same time it demands its fair share of intellectual engagement because the language tends to get (necessarily) intricate. And if you’re wondering: There are no equations.

In fact, I would be able to describe the experience of reading Dreams of a Final Theory using a paragraph from the book, and such internal symmetry is unmistakable throughout the book:

But why should the final theory describe anything like our world? The explanation might be found in what [Robert] Nozick has called the principle of fecundity. It states that the different logically acceptable universes all in some sense exist, each wit its own set of fundamental laws. The principle of fecundity is not itself explained by anything, but at least it has a certain pleasing self-consistency; as Nozick says, the principle of fecundity states ‘that all possibilities are realized, while it itself is one of those possibilities’.

Buy the book.

'Nothing in the history of science is ever simple'

Once I finished Steven Weinberg’s book Dreams of a Final Theory, I figured I’d write a long-winding review about what I think the book is really about, and its merits and demerits. But there is a sentence in the seventh chapter – titled ‘Against Philosophy’ – which I think sums up all that the book essentially attempts to explain.

Nothing in the history of science is ever simple.

And Dreams of a Final Theory wants to make you understand why that is so. To Weinberg’s credit, he has done a good job – not a great one – with complexity as his subject. I say ‘not a great one’ because it has none of the elegance that Brian Greene’s The Elegant Universe did, and it laid out string theory from beginning to end. At the same time, it is still Weinberg, one of the towering figures of particle physics, at work, and he means to say, first, that there is no place for simplicity in his line of work and, second, even in all the terrible complexity, there is beauty.

The book, first published in 1992, is a discourse on the path to a ‘final theory’ – one theory to rule them all, so to speak – and the various theoretical, experimental, mathematical and philosophical challenges it presents. Weinberg is an erudite scientist and you can trust him to lay out almost all facets of all problems that he chooses to introduce in the book – and there are many of them. Also, I wouldn’t call the book technical, but at the same time it demands its fair share of intellectual engagement because the language tends to get (necessarily) intricate. And if you’re wondering: There are no equations.

In fact, I would be able to describe the experience of reading Dreams of a Final Theory using a paragraph from the book, and such internal symmetry is unmistakable throughout the book:

But why should the final theory describe anything like our world? The explanation might be found in what [Robert] Nozick has called the principle of fecundity. It states that the different logically acceptable universes all in some sense exist, each wit its own set of fundamental laws. The principle of fecundity is not itself explained by anything, but at least it has a certain pleasing self-consistency; as Nozick says, the principle of fecundity states ‘that all possibilities are realized, while it itself is one of those possibilities’.

Buy the book.