Astronomy and Space

CSA astronaut Chris Hadfield just recently concluded his...

abhimat — Sun, 12 May 2013 22:17:26 -0700

CSA astronaut Chris Hadfield just recently concluded his position as commander of the ISS and is about to return back to Earth aboard a Soyuz spacecraft. Before departing, he performed this beautiful version of David Bowie’s Space Oddity as a way of saying goodbye to the ISS.

Have to say, Chris Hadfield, among his other roles, did a wonderful job of publicizing the ISS’s activities.

Where do the Fermi Bubbles come from?

abhimat — Mon, 29 Apr 2013 20:21:00 -0700

In 2010, data from the Fermi Large Area Telescope revealed a large new structure that appeared to be part of the Milky Way: two giant bubbles, emitting in gamma-ray, extending about 10 kpc out of the galactic center away from the Milky Way’s plane. While the discovery itself was momentous (compared to finding a new continent on Earth), a more interesting challenge has been explaining the existence of these bubbles. There isn’t a very obvious solution to why these bubbles exist.

Since the Fermi Bubbles appear to be centered at the galactic center, it suggests that their formation would likely be related to the objects located at the galactic center. Currently, there are two popular proposed explanations for the existence of the bubbles: one relying on the supermassive black hole at the center of the Milky Way, Sgr A*, and the other depending on the wind produced by a high rate of star formation at the galactic center. Both models rely on producing a large amount of gas that can flow out of the Milky Way at a high pressure.

Sgr A* may have been a messy eater

We have evidence for nearly all large galaxies possessing a supermassive black hole in their centers (see this previous post). A subset of these black holes are active, meaning that we can observe a large amount of emission leading out from the centers of their host galaxies. The emissions originate from disks of gas surrounding the black hole and often being expelled in the form of jets. This gives the centers of these galaxies the name Active Galactic Nuclei, or AGN.

Sgr A* is the Milky Way’s supermassive black hole, with a mass about four million times that of the Sun, but it is not currently active. However, the black hole could have been active in the past. If a star ventures too close to the black hole, it could be tidally disrupted. This means that the tidal forces¹ resulting from the supermassive black hole rip apart the star, and the resulting matter settles into a disk around the black hole. A portion of the accreting matter can then be expelled along jets shooting in opposite directions away from the black hole.

In the past there could have been periods when a large amount of gas or a star ventured too close to Sgr A*. The resulting jets formed from the interaction between these and the black hole could then have provided the energy necessary to construct the bubbles by expelling a large amount of gas from the Milky Way center.

Starbursts, but not the candy kind

Besides jets originating from Sgr A*, the galactic center could have also gone through a period of intense star formation, classifying it as a starburst region. During a starburst period, a large number of massive stars are born. These massive stars then quickly burn through their fuel and die through a supernova. If many supernovae take place close together, their shock waves create a wind of gas emanating from the galactic center region. This wind could also provide the necessary amount of energy required to create the Fermi Bubbles.

Making radiation from bubbles

Both scenarios can create expanding bubbles at the sizes required for the Fermi bubbles. Upon making the bubbles, the scenarios also have to account for the radiation we observe from the bubbles. Although each method has its subtleties, broadly, both rely on a very similar method: a shock between the gas inside the bubble and the interstellar medium surrounding it.

As the bubbles expand, the pressure inside the bubbles drops. At a certain point, the pressure at the edge of the bubbles reaches the pressure of the surrounding medium (essentially, the speed of the particles in the bubbles drops to below the speed of sound in the surrounding medium at this point). This results in the formation of a shock wave.

As explained by these models, the shock waves are the Fermi Bubbles that we observe. The radiation outlining the bubble is created through the inverse Compton scattering process. The low energy and large wavelength photons in the interstellar medium meet with the high velocity electrons at the shock wave. The low energy photons (from the radio and infrared portion of the spectrum) can collide and be scattered to higher energies, using some of the energy from the electrons. This leads to radiation in the gamma ray portion of the spectrum, which we can observe as the Fermi Bubbles.

While both models so far appear to help satisfy the constraints set by observations, there still is no clear leader among them. More observations are still necessary to help decide which is the likely explanation for blowing these bubbles.

Sources and Further Exploration

Carroll, Bradley W. and Dale A. Ostlie. “An Introduction to Modern Astrophysics”, 2007 (2nd Ed.), Pearson Education, Inc.
Cheng, K.S., D.O. Chernyshov, V.A. Dogiel, et al. “Origin of the Fermi Bubble”, 2011, ApJ 731:L17-20.
Lacki, Brian C. “The Fermi Bubbles as starburst wind termination shocks”, 2013, arXiv:1304.6137v1.
Kohler, Susanna. “Blowing Bubbles from Our Galaxy”, 26 April 2013, astrobites.
Olmstead, Alice. “No jets in the Galactic Center?”, 22 January 2013, astrobites.
Su, Meng, Tracy R. Slatyer, and Douglas P. Finkbeiner. “Giant gamma-ray bubbles from Fermi-LAT: active galactic nucleus activity or bipolar galactic wind?”, 2010, ApJ 724:1044-1082.

Image Credits

Fermi Bubble Illustration: NASA/GSFC

A tidal force occurs when the force of gravity is not uniform across an entire object. The side of an object near a massive body will feel a stronger gravitational pull than the side further away from the body. Because of this difference in forces, the object feels as if it is being pulled apart. ↩

Who Killed The Deep Space Climate Observatory?

abhimat — Thu, 25 Apr 2013 23:31:57 -0700

Who Killed The Deep Space Climate Observatory?:

Politics and bureaucracy can get very ugly and have sad results.

On dark matter

abhimat — Thu, 25 Apr 2013 17:49:31 -0700

On dark matter:

Alexander B. Fry, an astronomy graduate student at UW Seattle, recently wrote this very accessible introduction to dark matter for Aeon Magazine. Especially useful after the announcement of these exciting results.

Dark Matter Search Results Using the Silicon Detectors of CDMS II

abhimat — Thu, 25 Apr 2013 17:44:38 -0700

Dark Matter Search Results Using the Silicon Detectors of CDMS II:

Some exciting news from the CDMS collaboration. They have found three separate events that correspond to a WIMP collision with 99.8% certainty. If you remember from the Higgs Boson discovery, the discovery status gets appointed at 99.9999% certainty. Although not quite there yet, this announcement is still very exciting. Astrobites has a nice overview of this paper here.

Rolling the dice: understanding how physicists hunt for the Higgs

abhimat — Mon, 22 Apr 2013 12:00:52 -0700

Rolling the dice: understanding how physicists hunt for the Higgs:

This is a bit delayed, but it presents a fantastic analogy for understanding how the detection of the Higgs Boson works.

Voyager

abhimat — Sun, 21 Apr 2013 12:01:06 -0700

Voyager:

Randall Munroe explores what it would take to retrieve the Voyager I spacecraft on his What If? blog.

Supernova left its mark in ancient bacteria

abhimat — Sat, 20 Apr 2013 19:23:31 -0700

Supernova left its mark in ancient bacteria:

Fascinating that we may be detecting iron from a 2.2 million year old supernova in fossilized remains of bacteria.

Braids in the Solar Corona

abhimat — Mon, 04 Mar 2013 20:29:16 -0800

Comparing the solar atmosphere with that of the Earth reveals an apparent contradiction. On the Earth, the atmosphere gets colder at higher altitudes. This is a result of thermodynamics: pressure decreases as the distance from the surface increases, allowing gas to expand and drop in temperature. Applying this to the Sun, however, would lead to the expectation that the temperature in the solar atmosphere would also drop with increasing altitude. However, we observe that the solar corona, the Sun’s outer atmosphere extending out millions of kilometers, in fact has a higher temperature (reaching 2-4 million Kelvin) than the gas layer underneath.

In order to resolve this contradiction, solar astronomers have theorized that the necessary heat comes from energy lost by the formation and unravelling of magnetic ‘braids’ in the corona. Until recently, though, observations confirming these braids had never been conducted. Observing the sun beyond 100,000 K requires studying ultraviolet and X-ray emissions. These wavelengths do not pass through the atmosphere, so conducting these observations requires placing imaging devices outside of the Earth’s atmosphere. So far, none of the instruments capable of imaging the sun at the required wavelengths had the necessary resolution that allowed studying the braid structures.

On 11 July 2012, a group of scientists launched Hi-C (the High-resolution Coronal Imager)¹ aboard a sounding rocket in order to reach an altitude where the necessary ultraviolet observations could be performed. While the imager fell to the Earth, it was able to collect about 5 minutes of observations of the solar corona at 1.5 million Kelvin, at a resolution of 0.2 arcsec (corresponding to about 150 km (!) on the Sun), enough to be able to resolve the braided structures.

The team was able to observe a few examples of braiding in the corona during the course of the short flight (a set of images from one event from the observation is shown below). There was evidence of not just the magnetic field braiding and loops twisting along their length, but also subsequently reconnecting following the braiding and leading to heating of the corona. The braiding itself is thought to be powered by convection effects on the magnetic field in the photosphere (the region of the Sun below its atmosphere).

Essentially, the braiding provides a mechanism for some of the energy in the magnetic fields of the Sun to be converted into heating the corona. These observations demonstrate that the braiding in the solar atmosphere can release enough energy to account for the corona’s higher temperature, heating the region up to 4 million Kelvin².

Sources and Further Exploration

Cirtain, J. W., Golub, L., Winebarger, A.R., et al. “Energy release in the solar corona from spatially resolved magnetic braids”, 2013, Nature 493:501-503.

Yet another imaginative astronomy acronym. I think I can start an entire blog devoted just to clever astronomy acronyms… ↩
The observations also help prove that this artwork by Lim Heng Swee on Threadless is slightly inaccurate.

Accuracy would be improved if the Sun were braiding its rays instead of combing them (this may or may not have contributed towards the inspiration for writing this post). ↩

Interplanetary Cessna

abhimat — Sun, 03 Feb 2013 20:55:43 -0800

Interplanetary Cessna:

A wonderful look into whether a plane could fly over different bodies in the solar system by Randall Munroe on the What If? blog.

Yeah, Venus is a scientifically interesting place, but definitely not a fun place…

Me presenting the research project I conducted over the summer...

abhimat — Sun, 03 Feb 2013 20:50:00 -0800

Me presenting the research project I conducted over the summer as part of the Cornell University REU program. This was at the 221st AAS meeting, held in early January at Long Beach, CA. The project involved studying the pulsar B2224+65, and its optical bow-shock nebula (The Guitar Nebula) and the X-ray jet coincident with the pulsar’s position. Details about the project, as well as a copy of the poster, are available here.

The entire AAS meeting was a blast, and a tad bit overwhelming (so much exciting astronomy!).

Recycling: How Pulsars Get a New Lease on Life

abhimat — Thu, 03 Jan 2013 18:24:00 -0800

Pulsars are, at least in my opinion¹, some of the most interesting objects in the universe. They are extremely dense stars, supported by neutron degeneracy pressure, shooting out beams of radiation along their magnetic axes. These extreme behaviors can both serve as tools, helping astronomers get a better sense of their surroundings, as well as laboratories, allowing astronomers to study extreme situations that may not be as easily observable in other locations in the universe. I recently wrote a post detailing briefly some of the important and interesting characteristics of pulsars. This post goes beyond that relatively simple look at pulsars. Instead, it focuses on a few of the neatest phenomena that take place in the lives of some very special pulsars that have orbiting companion stars, helping deviate their behaviors from those of ordinary pulsars.

A Shocking Discovery

The first millisecond pulsar discovery (known as PSR B1937+21) took place in 1982 by Don Backer and Shrinivas Kulkarni from the Radio Astronomy Lab at UC Berkeley. Previous observations had suggested two different objects in this position of the sky, with the compact object out of these two possibly being a pulsar with a period shorter than 10 ms. To hunt out the pulsar, the team of radio astronomers implemented subsequently higher and higher sampling rates to increase the frequency range of their search. Ultimately, a pulsar was discovered, with a period of just 1.558 ms.

To truly appreciate how shocking this result appeared at the time (and still is), recall that pulsars are neutron stars with masses on the order of that of the Sun, and have radii on the order of 10 km. The fastest pulsars known at the time had periods of a little less than a second, spinning just a few times every second. To create pulses less than every 10 ms, one of these stars has to be spinning more than hundred times a second. Even more mind-blowing is the fact that on the surface of the neutron star, matter is traveling at velocities of 0.13c (that’s 0.13 times the speed of light!) Furthermore, the short period puts it very close to the spin rate limit of 2000 Hz (the pulsar’s rate is 642 Hz) where centrifugal forces would begin to exceed the gravitational force on the star’s surface and rip it apart.

The biggest questions resulting from the discovery centered around how the pulsar was formed and what gave it its millisecond period. Pulsars’ spin rates slow down over time as they lose energy (known as their spin-down rates), and this can be determined by measuring changes in the period of the pulses coming from pulsars. Just using this pulsar’s spin-down rate and assuming a maximum possible spin rate of 2000 Hz, the pulsar would only have been about 750 years old! Yet, no supernova remnants could be found in the area, as would have been expected for a pulsar this young. All of this suggests that the pulsar, and its millisecond period, was not the direct result of a supernova. Something else must have resulted in giving it its short period.

The Current Picture

The model for the formation of millisecond pulsars most widely supported today centers around binary objects. In a binary star system, the more massive star first undergoes a supernova. In the process, the star system could disrupt, meaning that the less massive star could be ejected due to the supernova, if the collapse is not symmetrical or due to its position in orbit. This case results in an ordinary, isolated pulsar, the same result as if there were just a solitary heavy star rather than a binary star system.

More interesting is if the binary system is not disrupted, and instead resulting in a young pulsar and its ordinary (main sequence) companion star. As time progresses, the pulsar evolves like all pulsars and its rotation period gets longer as it loses energy. However, the companion star is also aging alongside the pulsar, and eventually it reaches the red giant phase, with a dense, white dwarf core and an atmosphere that extends out to a further distance as it becomes older. The pulsar’s gravitational attraction begins to pick off matter off of the companion star’s atmosphere, and this material starts accreting onto the neutron star. The gravitational energy of the accreting matter is released through thermal emission in X-ray, while the angular momentum of the orbiting companion star is converted into the angular momentum of the star’s rotation. This causes the star’s rotation to speed up, rotating hundreds of times every second, and making it millisecond pulsar.

The process gives millisecond pulsars their other name: recycled pulsars. If not for a orbiting companion, a pulsar would rotate more slowly and eventually lose brightness as it ages, eventually becoming non-observable. However, the presence of a companion makes the pulsar spin up again, this time much faster, and results in a greater brightness.

Going back to our binary star system again, something interesting can happen at this stage as well as the system encounters another fork in the road. The companion to the pulsar itself could be massive enough to undergo a supernova explosion, and become a second pulsar in the system. Again, if the explosion is not symmetrical enough, the two pulsars can get separated. However, if the system isn’t disrupted, we can expect to find two pulsars orbiting one another: one of them being an ordinary young pulsar (with a relatively long period) and the other being a recycled (millisecond) pulsar. The exciting part of this result is that if the beams of both pulsars happened to hit the Earth, we could see two pulsars in the same spot of the sky, each with different periods. It turns out that we do have observational evidence for the existence of a system like this. The double pulsar system PSR J0737-3039 has an ordinary pulsar and a millisecond pulsar with beams that happen to both point towards the Earth. Typically, though, the younger pulsar fades away quickly, so we aren’t always lucky enough to be able to view both. In fact, the younger component of the PSR J0737-3039 faded away in 2010 and is no longer observable.

A Bit of Stamp Collecting²

One useful way to organize discovered pulsars is to plot them by two of their most easily observed characteristics: their periods and period derivatives (the rate at which the period is changing). This diagram (shown above), a \(P-\dot{P}\) diagram, is especially useful to gain a sort of visualization of a pulsar’s life cycle. The diagram plots discovered pulsars based on the two characteristics. The period is plotted along the horizontal axis, while the period derivative is on the vertical axis. It turns out that these characteristics are enough to determine a pulsar’s age and their energy output, both of which are plotted in the diagram as diagonal dotted lines.

Pulsars typically begin life in the big clump in the upper portion of the diagram, starting with high energy outputs (left side of the big clump) and often with observable supernova remnants associated with them. As they get older, they migrate towards the right side of the clump, slowly diminishing their energy output and entering the portion of the diagram affectionately labelled the ‘Graveyard’. However, if the pulsars are in binary systems, they can cheat death and avoid the Graveyard by the accretion of matter. This speeds up their spins, and the resulting pulsars migrate towards the bottom left of the diagram, where the recycled millisecond pulsars reside. Notice that most of these are found in binary systems, helping support the binary system model for their formation.

Black-Widows

There’s one subset of the millisecond pulsar population that is extremely interesting: the black-widow pulsars. These pulsars have very low mass companion stars, masses on the order of 1 percent of the Sun’s mass. A companion’s atmosphere spreads out to large distances, and leads to large portions of the companion star’s mass to be absorbed by the pulsar. Since the pulsar is “eating” its companion, they have been named black-widow pulsars³. This can be seen in optical wavelengths since the side of a companion star facing the pulsar is much brighter and leads to measurable changes in brightness as the companion and pulsar orbit around each other. Most of these black-widows are found in globular clusters, which have high densities of stars, suggesting that their system formations are due to the original companion stars being swapped for much less massive companions.

What’s more interesting about these stars is that they can serve as useful scientific laboratories. The black-widow pulsars for which masses can be measured tend to be very massive⁴. PSR B1957+20 is believed to have a mass of 2.40 solar masses, while the newly discovered PSR J1311-3430 is thought to come in at around 2.7 solar masses. These values are about double of most other pulsars. The massive, and dense stars, can help provide some clues about how matter behaves at very extreme densities, one of the areas of physics which is still not very well understood. Conditions with densities a little higher than those found in atomic nuclei and very high temperatures can be created with particle colliders, but even higher densities at low temperatures can only be found inside neutron stars so far. Studying the behavior of these black-widows could provide valuable constraints on the Equation of State of dense matter, and either support or disprove some of the theories describing matter in that realm.

It isn’t often that astronomy can provide constraints on physics. Often, to test new physics theories, experiments are constructed on the ground. Ground experiments can be better and more easily controlled while measurements are often easier to obtain. Pulsars themselves are often just used as scientific tools. They are often implemented as probes to determine the density of the interstellar medium, or used as very precise clocks to help conduct tests on relativity or detect gravitational waves. While those are exciting, the high densities inside neutron stars can make them one of the few areas of astronomy that can help give back to physics, making them laboratories as well as tools. This is an opportunity where instead of using physical laws to understand more about the universe, astronomers could help define those very laws.

Sources and Further Exploration

Backer, D. C., Kulkarni, Shrinivas R., and Heiles, Carl. “A millisecond pulsar”, 1982, Nature 300:615-618.
Lyne, Andrew and Francis Graham-Smith. “Pulsar Astronomy”, 2012 (4th Ed.), Cambridge University Press.
van Kerkwijk, M.H., Breton, R.P., Kulkarni, S.R. “Evidence for a massive neutron star from a radial-velocity study of the companion to the black-widow pulsar PSR B1957+20”, 2011, ApJ 728:95-102.
Kramer, M. and Stairs, I.H.. “The Double Pulsar”, 2004, Annu. Rev. Astron. Astrophys. 46:541-72.
Phinney, E. S. and Kulkarni, S.R. “Binary and Millisecond Pulsars”, 1994, Annu. Rev. Astron. Astrophys. 32:591-639.
Pletsch, H.J., Guillemot, L., Fehrmann, H., et al. “Binary millisecond pulsar discovery via gamma-ray pulsations”, 2012, Science 338:1314-1317.
Radhakrishnan, V. and Srinivasan, G. “On the origin of the recently discovered ultra-rapid pulsar”, 1982, Current Science 51:1096-1099.
Romani, Roger W., Filippenko, Alexei V., Silverman, Jeffrey M., et al. “PSR J1311-3430: A heavyweight neutron star with a flyweight helium companion”, 2012, ApJ 760:L36-41.
Stairs, Ingrid H. “Pulsars in Binary Systems: Probing Binary Stellar Evolution and General Relativity”, 2004, Science 304:547-552.

Image Credits

\(P-\dot{P}\) Diagram: “Handbook of Pulsar Astronomy” by Lorimer & Kramer.

I may be a little biased by my current research project at Berkeley. I’m working on an automatic pipeline to search and study pulsars in the same field of view as the Kepler spacecraft and around the galactic center. ↩
Although astronomy is mostly physics, stamp collecting tends to creep in a little bit. ↩
I have to abandon one of my original premises when starting the blog: astronomers do not give very imaginative names. Writing on this blog has given me plenty of evidence to the contrary (another notable example: the Musket Ball Cluster). ↩
There isn’t a very well supported explanation yet why black-widow pulsars tend to be more massive. ↩

Leap Seconds

abhimat — Wed, 02 Jan 2013 14:44:00 -0800

Leap Seconds:

This week on the What If? blog by Randall Munroe of XKCD fame: A fascinating consideration of how it might be possible to reverse the effects that are corrected by adding leap seconds.

(Since I’m currently also working on a post about millisecond pulsars, I can’t help but think of the parallel for pulsars where the neutron stars spin-up by accreting more matter.)

2012: My Favorite Doomsday Scenarios

abhimat — Mon, 31 Dec 2012 17:06:01 -0800

2012: My Favorite Doomsday Scenarios:

Fun, and factually correct, look at some interesting apocalyptic scenarios as 2012 comes to a close.

A (Somewhat) Brief Background on Pulsars

abhimat — Tue, 18 Dec 2012 20:47:48 -0800

I am currently writing a post about binary pulsar systems, recycled pulsars, and a very interesting group of pulsars called “Black Widows”. In the process, I realized that I don’t currently have a good summary of what pulsars are on the blog (and the binary pulsars post was getting a bit lengthy), so I took out much of the pulsar and neutron star background from the post and started this new post with it. So while waiting to read about how some of the most interesting objects in the universe get even more interesting, here’s a bit of background on those interesting objects.

It all begins with a bang!

Typically, when a star exhausts its source of energy, it has three different endings available to it that depend on its mass: becoming a white dwarf, a neutron star, or a black hole. The lighter stars, like the Sun, eventually become white dwarfs, while the heaviest result in black holes. For now we’re interested in the stars in the middle, though, those between about 8 and 20 solar masses.

For a sun-like star, once the nuclear fuel gets exhausted a complete collapse is prevented as the electron degeneracy pressure still helps support the core of the star, resulting in a white dwarf. However, for more massive stars, the core’s mass, between 1.9 and 2.5 solar masses, cannot be supported by the electron degeneracy pressure. The only thing stopping the collapse is neutron degeneracy pressure in the core. In the process, the rest of the star’s mass begins to fall towards the center of the star, and the lost gravitational energy is expelled in a supernova.

Almost the entire star is torn apart and expelled in the violent process, but what’s left behind is that dense core held up by neutron degeneracy pressure: a neutron star. A neutron star can be simply viewed as a giant nucleus. Its mass is just a little more than our Sun’s (typically about 1.4 solar masses), but that mass is compressed into a radius of about 10 km, the size of a city. This gives neutron stars densities on the order of 10¹⁴ g cm^-3, the same order of magnitude for the density of an atomic nucleus. That mass is made up primarily of neutrons, with about 5% protons and electrons.

In the process, the angular momentum of the original star has to be conserved. As the radii of these large and massive stars shrinks down to the tiny city size radii of the neutron stars, the angular velocity has to increase to conserve angular momentum, meaning that the resulting neutron star starts spinning much faster than the original, larger star. This results in neutron stars with rotational periods usually about 0.1 seconds or lower. As they gradually lose energy over time, their rotation periods increase as well.

Cosmic Lighthouses

If that was all there was to neutron stars, they wouldn’t be terribly exciting. Due to their temperatures, they would only radiate at X-Ray wavelengths (from black body radiation), and would subsequently be difficult to observe. But the fun doesn’t have to quite stop just yet.

Pulsars are strongly magnetized neutron stars, with magnetic fields on the order of 10¹⁰ - 10¹² Gauss. This magnetic field is thought to be strong enough to lift some charged material off the surface of the neutron star and expel it along its magnetic fields¹. The accelerating particles lead to radiation, creating beams visible in radio frequencies.

Just as the Earth’s magnetic axis is not aligned with its rotation axis, the magnetic axes of pulsars are generally not aligned with their rotation axes as well. As a pulsar spins, its magnetic axis spins as well, rotating the radio beams along with it. If the radio beams happen to hit the Earth, we can see them as periodic blips, just as a ship sees a lighthouse’s rotating beams. In effect, pulsars are like cosmic lighthouses².

Both Scientific Tools and Laboratories

These basic traits of pulsars allow for some interesting uses as well, allowing their utility to spread beyond just neat artifacts of massive stars. The simple periodic blips can be used as clocks. Some pulsars are very stable and have accuracies that rival those of modern atomic clocks. These pulsars can allow studying distant regions in the galaxy. One interesting area is the galactic center. Although no pulsar has yet been discovered close to the center of the galaxy, the future discovery of one could help perform experiments on the gravitational field near a supermassive black hole. We can’t launch and deliver a clock to the galactic center and then observe it, but if we are able to find a pulsar, it would be like conveniently finding an observable clock right where we need it. In this way, a pulsar can be like a tool letting us study interesting phenomena in their habitats.

Furthermore, pulsar interiors are extreme environments, with intense amounts of pressure and high densities, and can act as laboratories to allow testing of physical theories, particularly the Equation of State of dense matter³. One method currently being developed right now is studying glitches. Glitches are when the period of the pulsar blips jumps suddenly. For young pulsars, a glitch can happen once every few years, becoming less frequent as pulsars age. The glitches are thought to be due to changes in the interior of the neutron stars. One of the more widely accepted models proposes that the neutron star crust and the inner neutron superfluid are mostly independent of each other, and a glitch occurs when angular momentum is trasferred in a rapid spasm to the crust. Characterizing observations of pulsar glitches can help strengthen or eliminate models of pulsar interiors, which, in turn, could help place constraints on the Equation of State of dense matter.

Sources and Further Exploration

Laskar, Tanmoy (ed.). “Radio Astronomy” astrobites.
Lyne, Andrew and Francis Graham-Smith. “Pulsar Astronomy”, 2012 (4th Ed.), Cambridge University Press.
Taylor, J. H. and D. R. Stinebring. “Recent Progress in the Understanding of Pulsars”, 1986, Annu. Rev. Astron. Astrophys. 24:285-327

Remember, the neutron star isn’t completely made up of neutral neutrons, but also a small amount of charged electrons and protons. These get picked up by the pulsar’s magnetic fields. Primarily, the less massive electrons are the particles that get sweeped up for the ride. ↩
Allowing astronomers to map the gravitational waves, just as a lighthouse lets seafarers safely traverse waves in the ocean…I might be pushing this analogy a bit too far. ↩
In fact, black widow pulsars, which are detailed in the upcoming binary pulsar systems post, have been proposed as possible laboratories to study the Equation of State of dense matter. ↩

It’s Carl Sagan’s birthday today. I like to honor him by keeping...

abhimat — Fri, 09 Nov 2012 00:10:19 -0800

It’s Carl Sagan’s birthday today. I like to honor him by keeping these words in mind.

"For all our failings, despite our limitations and fallibilities, we humans are capable of greatness."

abhimat — Fri, 09 Nov 2012 00:05:28 -0800

“For all our failings, despite our limitations and fallibilities, we humans are capable of greatness.”

- Carl Sagan

Free Advice

abhimat — Sun, 04 Nov 2012 22:48:18 -0800

Free Advice:

Some great advice related to a certain letter that has been gaining a bit of publicity in the Astronomy community. This has been the most thoughtful response that I have read so far to the letter. Although the piece is not aimed towards an undergraduate audience, I found some valuable lessons that will certainly be helpful for what seems to be the career that I am currently aiming towards.

Using the Mars Hand Lens Imager (MAHLI), Curiosity snapped 55...

abhimat — Sun, 04 Nov 2012 22:40:49 -0800

Using the Mars Hand Lens Imager (MAHLI), Curiosity snapped 55 high-resolution images of itself at “Rocknest”. The first four scoops sampled by the rover can be seen in the lower left portion of the image. Self portraits (like this one) are important to keep track of the rover’s condition. The engineers working with the rover can understand how its different parts are changing over time.

Curiosity’s thoughts while taking this picture: “Damn, I look fine.”

The Higgs, Boltzmann Brains, and Monkeys Typing Hamlet

abhimat — Sun, 04 Nov 2012 22:26:17 -0800

The Higgs, Boltzmann Brains, and Monkeys Typing Hamlet:

The example I am showing you here demonstrates yes, if you “go to infinity”–whatever that means in the real world–you can “prove” almost anything you like!

A fascinating piece discussing one of the wildest concepts in physics (Boltzmann Brains) and why the concept is likely not of much utility.

Astronomy and Space

CSA astronaut Chris Hadfield just recently concluded his...

Where do the Fermi Bubbles come from?

Sgr A* may have been a messy eater

Starbursts, but not the candy kind

Making radiation from bubbles

Sources and Further Exploration

Image Credits

Who Killed The Deep Space Climate Observatory?

On dark matter

Dark Matter Search Results Using the Silicon Detectors of CDMS II

Rolling the dice: understanding how physicists hunt for the Higgs

Voyager

Supernova left its mark in ancient bacteria

Braids in the Solar Corona

Sources and Further Exploration

Interplanetary Cessna

Me presenting the research project I conducted over the summer...

Recycling: How Pulsars Get a New Lease on Life

A Shocking Discovery

The Current Picture

A Bit of Stamp Collecting2

Black-Widows

Sources and Further Exploration

Image Credits

Leap Seconds

2012: My Favorite Doomsday Scenarios

A (Somewhat) Brief Background on Pulsars

It all begins with a bang!

Cosmic Lighthouses

Both Scientific Tools and Laboratories

Sources and Further Exploration

It’s Carl Sagan’s birthday today. I like to honor him by keeping...

"For all our failings, despite our limitations and fallibilities, we humans are capable of greatness."

Free Advice

Using the Mars Hand Lens Imager (MAHLI), Curiosity snapped 55...

The Higgs, Boltzmann Brains, and Monkeys Typing Hamlet

A Bit of Stamp Collecting²