Pulsars, Dame Jocelyn Bell Burnell, and Pioneer


The image above depicts a plaque that was attached to the Pioneer 10 and Pioneer 11 space probes sent out in the early 1970s. The idea was that someone who found the plaque later would be able to get an idea of who sent the space probe out and where they were. In case you’re wondering about the nude character studies, this is what a NASA committee thought would be the most appropriate picture of our species. Occupy Math is happy that they included a woman at all. It is the “location function” of the plaque that inspired today’s post, but we also have an inappropriate Nobel prize and a type of stellar monster to talk about. Interested? Read on!


A neutron star is a burned out remnant of a regular star. Since its nuclear burn is over, radiation cannot keep the star all spread out. Without radiation pressure to keep it inflated, the star’s gravity crushes it so hard that the electrons and protons in its atoms are placed in contact and become neutrons. Neutron stars are more massive than white dwarfs and smaller than stars that become black holes.

Here is a very interesting thing about neutron stars. When they collapse into neutronium, the conservation of that parent star’s spin means that the neutron star spins really fast. The neutron star also has a huge magnetic field. Since their spin and magnetic axes do not line up, the star emits a rotating cone of powerful radio energy. If that cone washes over your position, you hear an incredibly regular signal at an extremely high power level. The neutron stars which beam signals that we can hear are called pulsars.


The Social Justice of Pulsars

Social justice? Yep, social justice. We have a problem with ignoring the contributions of, among other groups, women. Jocelyn Bell Burnell noticed pulsars as a graduate student, found multiple examples in the data from a radio telescope she was overseeing, and was second author on the paper announcing that one of Einstein’s theoretical monsters had been directly observed. The first author was her thesis advisor who split the 1974 Nobel Prize for this work. Dr. Burnell was mentioned in the citation, but left out of the prize. When “Miss” Burnell made her discovery, in Britain, women did not win science prizes. They kept house and had children. The whole notion that a woman should be included was simply foreign to the academic community at the time.

Dr. Burnell has a remarkably good attitude about this situation, and Occupy Math noticed her because of the announcement that her work has been awarded a $3,000,000 prize. The world is becoming better as time winds its way from chaos to entropy. Dr. Burnell, who currently teaches astronomy at Oxford University, says she is not bothered by it. Explaining that she is a Quaker who lives a simple life, the money will go to creating scholarships for people from underrepresented backgrounds who want to study physics. The funds will be administered by the U.K.’s Institute of Physics, and Dr. Burnell is hopeful that having a more diverse array of people entering the field will lead to even more new discoveries. Applause!


What about Pioneer 10 and 11?

The left hand side of the plaque, repeated above, includes a whole bunch of lines interrupted by hash marks. Those are the pulse patterns of fourteen pulsars and should give a technological society the ability to locate earth. The math needed is very similar to that used to establish the latitude of a wooden sailing ship by shooting the stars. The pulsar patterns unambiguously locate earth for any future civilization that finds the plaque.

Including these navigational directions, and even the plaque itself, represented unparalleled optimism. The Pioneer probes are not really going that fast. The following quote from the Wikipedia article on Pioneer 10 gives a nice perspective.

If left undisturbed, Pioneer 10 and its sister craft Pioneer 11 will join the two Voyager spacecraft and the New Horizons spacecraft in leaving the Solar System to wander the interstellar medium. The Pioneer 10 trajectory is expected to take it in the general direction of the star Aldebaran, currently located at a distance of about 68 light years. If Aldebaran had zero relative velocity, it would require more than two million years for the spacecraft to reach it.

Those worried about us sending directions for our home to possible aggressors need not worry. This point actually came up in an online argument where someone accused NASA of lacking “street smarts”. Occupy Math pointed out that a million years from now we will be far beyond human or, possibly, extinct. Any alien teams sent in response to the plaque will be archaeological, not conquest-oriented.


Little Green Men

When pulsar signals were first detected — incredibly powerful radio signals from deep space with regular pulse intervals — one of the hypotheses framed was that these were signals from an alien civilization: little green men. The signals were referred to as LGMs for a time, until the correct explanation of collapsed stars was framed. The search for intelligent life in the universe continues, but pulsars turn out to be a natural phenomenon.

Robert L. Forward was a physicist and science fiction writer. His books in the Dragon’s Egg series are set on the surface of a neutron star. It may be possible that neutrons have their own chemistry and can support life. Forward’s novels visit a neutron star and record its history, including first contact with humans. It is a good piece of fiction with solid physics, if you want more of a sense of these cosmic oddities.

Occupy Math hopes you have enjoyed this detour into physics with a side order of respect for our colleagues who happen to be women. As always, Occupy Math would like pointers to things that might make a good post. Please mail me at dashlock@uoguelph.ca or say something in comments!

I hope to see you here again,
Daniel Ashlock,
University of Guelph,
Department of Mathematics and Statistics


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