Monthly Archives: February 2013

Extreme Astrophysics as Food

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Pulsars are some of the most exotic objects detected by the Fermi satellite. They are a special kind of neutron star, ultra-dense remnants of very massive stars whose lives end in supernovae. They are about 10 km in radius and have the mass of ~1.5 Suns. They rotate very quickly -- they spin once every 0.001-100 seconds! -- and have very strong magnetic fields. They emit over a wide range of energies, including radio emission and the gamma rays seen by the LAT. Pulsars are tilted (like the Earth); their rotation and magnetic axes are offset, and so their radiation appears to pulse as it crosses our line of sight. About 25% of pulsars detected by Fermi are "radio quiet" and seen only in gamma rays.
Cake by Sylvia Zhu, David Green and Judy Racusin. Pulsar Technical Consultant was Megan DeCesar
The 2013 AAS Rossi prize was awarded to Alice Harding (GSFC) and Roger Romani (Stanford) for their work on gamma-ray pulsar modeling. So when it came time to enter the "Science as Food" competition in the annual Goddard poster party, it seemed only fitting to create a tribute to pulsars -- in cake form.

For our pulsar cake, the "neutron star" was a hemispherical vanilla cake with Swiss buttercream frosting. The cake was very dense, but not as dense as a real neutron star (a teaspoon of neutron star would weigh more than a mountain!). The surface of a real neutron star sometimes cracks under the strains of rapid rotation and large magnetic field. To show this cracking, the cake surface was covered in thin pieces of poured sugar (similar to Jolly Ranchers) and sugar crystals.

The radio emission sweeps around like a lighthouse beam as a pulsar rotates, and comes out from the magnetic poles. The radio beam was represented by a cone of styrofoam covered in fondant, and was the only nonedible part of the cake. The magnetic field lines also start from the magnetic poles; ours were made of pulled sugar, like candy canes. In a real pulsar, the closed field lines would not have been so tight and close to the neutron star (but real pulsars don't have to worry about fitting everything onto a cake stand).

The light cylinder is defined by the radius at which the magnetic field lines would have to travel at the speed of light in order to co-rotate with the neutron star. The gamma rays that Fermi observes originate in the outer magnetosphere near the light cylinder; we represented these regions with purple cotton candy. (This turned out to be an unfortunate choice given the surprising warmth and humidity of the day.) The entire setup was placed on a rotating cake stand; we were able to safely spin our pulsar at a speed of a few rotations per second.

After the judging process (we won the contest, although -- in the interest of full disclosure -- there was only one other entry) we removed the field lines and sliced up the neutron star. The cake pieces were all eaten within a few minutes. And although our pulsar cake was only a cartoonish representation of a pulsar, it was certainly much more delicious than a real pulsar would have been.