Type 1a supernova spotted in M82

(A version of this piece appeared on The Hindu, Chennai, website on January 22 as written by me.)

A Type 1a supernova was spotted a few hours ago by stargazers in the starburst galaxy M82, which is only 11.4 million light-years away from Earth (here’s an interactive map and a helpful sky-chart). This is the closest such supernova that has been detected since 1972, and is poised to give astronomers and cosmologists some invaluable insight into how such stellar explosions pan out, and what we can learn about neutrinos, gamma rays and dark energy from them.

See the bright, blinking spot of light on the galaxy's 'lower' half? That's your SN1a.
See the bright, blinking spot of light on the galaxy’s ‘lower’ half? That’s your SN1a. Animation by E. Guido, N. Howes, M. Nicolini

The supernova is a Type 1a supernova (SN1a), which means it’s not the explosion that happens when a star runs out of fuel and blows itself apart. Instead, it’s what happens when a white dwarf pulls in too much material from a nearby star and blows itself apart—having bitten off more than it could chew.

That M82 is a starburst galaxy means it’s rapidly producing stars. This also means it has a lot of old stars, many of which are continuously dying. They could either be dying as Type 2 supernovae—which is the run-out-fuel kind—or Type 1. The SN1a that’s gone off now (i.e. so many millions of years ago) has chosen to go off as Type 1a, and that’s a good thing because we haven’t spotted a Type 1a since 1972 that’s so close.

When the explosion releases light, it doesn’t immediately start its journey and head straight for Earth. Instead, the light gets trapped in the explosion behind lots of matter, and is delayed. In fact, the ‘ghost particles’ that can pass through matter almost undetected, neutrinos, get a headstart. They reach us before light from the explosion does.

However, a Type 1a supernova produces far fewer neutrinos than does a Type 2, so while the neutrinos flying our way will still be valuable, they might not be valuable enough to study a supernova with. On the other hand, the M82-SN1a could be our big chance to study SN-origin gamma rays in the best detail for the first time in more than four decades.

However, since we haven’t had our detectors trained for neutrinos from M82 particularly, how do we know when that white dwarf in M82 blew up? We measure how its brightness varies over time. Using that information, we know the thing blew up 11.4 million years ago. Because a 1a’s variation of brightness over time consistently follows a well-established pattern, white dwarfs across the universe can be used as cosmic candlesticks: astronomers use them to judge the relative distances of nearby objects.

In fact, white dwarfs did play an important role in astronomers discovering that the universe was expanding at an accelerating rate due to dark energy. Paraphrasing astronomer Katharine Mack’s tweet: “With a better estimate of the distance [as judged from their brightness], we get a better link between the distance and the universe’s expansion.”

M82’s relative closeness is useful because it provides a lot more information to work with before it could get (more) adulterated through the distance of space. In fact, according to astronomer Daniel Fischer, the supernova’s been going on for a full week now, and was missed by the bigger budget telescopes because it was, and I quote, ‘too bright’. As Brad Tucker, an astronomer from Berkeley, tweeted,

So, hadn’t it been for amateur astronomers, who’ve made this remarkable observation, too, we wouldn’t have spotted this beauty. Already, according to Skymania’s Paul Sutherland, astronomers believe they’ve caught this supernova early in its act and think it could brighten even further.

This particular find was made by Russian amateur astronomers on January 22, and later confirmed by multiple sources. In fact, M82-SN1a seems to have appeared in the photographs taken by noted Japanese amateur astronomer Koichi Itagaki on January 14 itself (beating Patrick Wiggins by a day). And if you’re interested in reporting such discoveries, check this page out. If you want to keep up with the social media conversation over M82, follow @astrokatie. She’s going nuts (in a good way).

Itagaki's photos of M82
Itagaki’s photos of M82

A useful book to have around

14oeb_Space_jpg_1719808fIndia’s Rise as a Space Power is a book by Prof. Udupi Ramachandra Rao, former Chairman, ISRO (1988-1994), that provides some useful historical context of the space research organization from a scientist’s perspective, not an administrator’s.

Through it, Prof. Rao talks about how our space program was carefully crafted with a series of satellites and launch vehicles, and how each one of them has contributed to where the organization, as such, is today: an immutable symbol of power in the Third World and India’s pride. He starts with the foundation of ISRO, goes on to the visions of Vikram Sarabhai and Satish Dhawan, then introduces the story of Aryabhata, our first satellite, followed by Bhaskara I and II, the IRS series, the INSAT program, the ASLV, PSLV and GSLV, and finally, the contributions of all these instruments to the Indian economy. The period in which Prof. Rao served as Chairman coincided with an acceleration of innovations at ISRO – when he assumed the helm, the IRS was being developed; when he left, development of the cryogenic engine was underway.

However, India’s Rise… leaves out that aspect of his work that he was most well-positioned to discuss all along: politics. The Indian polity is heavily invested in ISRO, and constantly looks to it for solutions to a diverse array of problems, from telecommunications to meteorology. While ISRO may never have struggled to receive government funding, its run-ins with the 11 governments in its 45-year tenure will have made for a telling story on the Indian government’s association with on of its most successful scientific/technological bodies. Where Prof. Rao makes comments, it is usually on one of two things: either to say discuss why scientists are better leaders of organizations like ISRO than administrators, or how foreign governments floated or sank technology-transfer deals with India.

… Mr. T.N. Seshan, who was the Additional Secretary in the Department of Space, a senior member of the negotiation team deputed under my leadership, made this trip [to Glavkosmos, a Soviet company that was to equip and provide the launcher for the first-generation Indian Remote Sensing satellites] unpleasant by throwing up tantrums just because he was not the leader of the Indian delegation. Subsequently, Prof. Dhawan had to tell him in no uncertain terms that any high-level delegation such as the above would only be led by a scientist and not an administrator, a healthy practice followed in [the Dept. of Space] form the very beginning. (pp. 124)

This aspect notwithstanding, India’s Rise… is a useful book to have around now, when ISRO seems poised to enter its next era: that of the successful use of its cryogenic engines to lift heavier payloads into higher orbits. It contains a lot of interesting information about different programs and the attention to detail is distributed evenly, if sometimes unnecessarily. There is also an accompanying collection of possibly rare photographs; my favorite shows a rocket’s nose-cone being transported by bicycle to the launchpad. Overall, the book makes for excellent reference, and thanks to Prof. Rao’s scientific background, there is a sound representation of technical concepts devoid of misrepresentation. Here’s my review of it for The Hindu.

And the GSLV flew!

The Copernican
January 6, 2014

Congratulations, ISRO, for successfully launching the GSLV-D5 (and the GSAT-14 satellite with it) on January 5. Even as I write this, ISRO has put out an update on its website: “First orbit raising operation of GSAT-14 is successfully completed by firing the Apogee Motor for 3,134 seconds on Jan 06, 2014.”

With this launch comes the third success in eight launches of the GSLV program since 2001, and the first success with the indigenously developed cryogenic rocket-engine. As The Hindu reported, use of this technology widens India’s launch capability to include 2-2.5 tonne satellites. This propels India into becoming a cost-effective port for launching heavier satellites, not just lighter ones as before.

The GSLV-D5 (which stands for ‘developmental flight 5′) is a variant of the GSLV Mark II rocket, the successor to the GSLV Mark I. Both these rockets have three stages: solid, liquid and cryogenic. The solid stage possesses the design heritage of the American Nike-Apache engine; the liquid stage, of the French Vulcain engine. The third cryogenic upper stage was developed at the Liquid Propulsion Systems Centre, Tamil Nadu—ISRO’s counterpart of NASA’s JPL.

There is a significant difference of capability based on which engines are used. ISRO’s other more successful launch vehicle, the Polar Satellite Launch Vehicle (PSLV), uses four stages: alternating solid and liquid ones. Its payload capacity to the geostationary transfer orbit (GTO), from which the Mars Orbiter Mission was launched, is 1,410 kg. With the cryogenic engine, the GSLV’s capacity to the same orbit is 2,500 kg. By being able to lift more equipment, the GSLV hypothetically foretells our ability to launch more sophisticated instruments in the future.

The better engine

The cryogenic engine’s complexity resides in its ability to enhance the fuel’s flow through the engine.

An engine’s thrust—its propulsive force—is higher if the fuel flows faster through it. Solid fuels don’t flow, but they let off more energy when burnt than liquid fuels. Gaseous fuels barely flow and have to be stored in heavy, pressurised containers.

Liquid fuels flow, have higher energy density than gases, and they can be stored in light tanks that don’t weigh the rocket down as much. The volume they occupy can be further reduced by pressurising them. Recall that the previous launch attempt of the GSLV-D5, in August 2013, was called off 74 minutes before take-off because fuel had leaked from the liquid stage during the pre-pressurisation phase.

Even so, there seems no reason to use gaseous fuels. However, when hydrogen burns in the presence of oxygen, both gases at normal pressure and temperature, the energy released provides an effective exhaust velocity of 4.4 km/s—one of the highest (p. 23, ‘Cosmic Perspectives in Space Physics’, S. Biswas, 2000). It was to use them more effectively that cryogenic engines were developed.

In a cryogenic engine, the gases are cooled to very low temperatures, at which point they become liquids—acquiring the benefits of liquid fuels also. However, not all gases are considered for use. Consider this excerpt from a NASA report written in the 1960s:

A gas is considered to be cryogen if it can be changed to a liquid by the removal of heat and by subsequent temperature reduction to a very low value. The temperature range that is of interest in cryogenics is not defined precisely; however, most researchers consider a gas to be cryogenic if it can be liquefied at or below -240 degrees fahrenheit [-151.11 degrees celsius]. The most common cryogenic fluids are air, argon, helium, hydrogen, methane, neon, nitrogen and oxygen.

The difficulties arose from accommodating tanks of super-cold liquid propellants—which includes both the fuel and the oxidiser—inside a rocket engine. The liquefaction temperature for hydrogen is 20 kelvin, just above absolute zero; for oxygen, 89 kelvin.

Chain of problems

For starters, cryopumps are used to trap the gases and cool them. Then, special pumps called turbopumps are required to move the propellants into the combustion chamber at higher flow-rates and pressures. Next, relatively expensive igniters are required to set off combustion, which also has to be controlled with computers to prevent them from burning off too soon. And so forth.

Because using cryogenic technology drove advancements in one area of a propulsion system, other areas also required commensurate upgrades. Space engineers learnt many lessons from the American Saturn launch vehicles, whose advanced engines (for the time) were born of using cryogenic technology. They flew between 1961 and 1975.

In the book ‘Rocket Propulsion Elements’ (2010) by George Sutton and Oscar Biblarz, some other disadvantages of using cryogenic propellants are described (p. 697):

Cryogenic propellants cannot be used for long periods except when tanks are well insulated and escaping vapours are recondensed. Propellant loading occurs at the launch stand or test facility and requires cryogenic propellant storage facilities.

With cryogenic liquid propellants there is a start delay caused by the time needed to cool the system flow passage hardware to cryogenic temperatures. Cryogenically cooled fluids also continuously vaporise. Moreover, any moisture in the same tank could condense as ice, adulterating the fluid.

It was in simultaneously overcoming all these issues, with no help from other space-faring agencies, that ISRO took time. Now that the Mark II has been successfully launched, the organisation can set its eyes on loftier goals—such as successfully launching the next, mostly different variant of the GSLV: the Mark III, which is projected to have a payload capacity of 4,500-5,000 kg to GTO.

While we are some way off from considering the GSLV for manned missions, which requires mastery of reentry technology and spaceflight survival, the GSLV Mark III, if successful, could make India an invaluable hub for launching heavier satellites at costs lesser than ESA’s Ariane program, which India used in lieu of the GSLV.

Good luck, ISRO!

Rethinking cryptocurrency

I’m still unsure about bitcoins’ uncertain future as far as mainstream adoption is concerned, but such issues have been hogging media limelight so much so that people are missing out on why bitcoins are actually awesome. They’re not awesome because they’re worth about $800 apiece (at the time of writing this) or because they threaten to trivialize the existence of banks. These concerns have nothing to do with bitcoins – they’re simply anti-establishment frustrations in post-recession era. Bitcoins, and other cryptocurrencies like it, are awesome because of their technical framework which enables:

  1. Public verification of validity (as opposed to third-party verification)
  2. Zero transaction costs (although this is likely to change)

Thinking about bitcoins as alternatives to dollars only five years into the cryptycurrency’s existence is stupid. Even scoffing at how steep the learning curve is (to learn about how to acquire and moblize bitcoins) is stupid. Instead, what we must be focusing on are the characteristics of the technology that makes the two mentioned techniques possible because they have great reformative potential in a country like India (if adopted correctly, which I suppose is a subjective ideal, but hey). Zero transaction costs enable individual and small enterprises to avoid painful scaling costs, while public verification enables only value to be transferred across a network instead of forcing two parties to share information unrelated ot the transaction itself with a bank, etc. Here’s my OpEd on this idea for The Hindu.