Meet: Elliott Bloom

Professor
Stanford Linear Accelerator Center (SLAC)
Stanford, CA

Who I Am

I am a Professor of Particle Astrophysics at Stanford University. I spend my research efforts at the Stanford Linear Accelerator Center, which is my home department. I began my career in accelerator based particle physics to study quarks and leptons and the strong and electro-weak force. I was a member of the team that first discovered quarks, via inelastic electron scattering experiments from the proton, at SLAC in 1968. About 12 years ago I became interested, through a Stanford course I developed for non-physics majors called "Cosmic Horizons", in the role that Gravity plays in forming the Universe.

What I Do

Over the past 10 years I have been building and doing space based experiments that study topics in Particle Astrophysics. My interests in Particle Astrophysics center on strong gravity, and the nature of dark matter. Regions of strong gravity, where General Relativity is relevant, are associated with neutron star and black hole candidate stellar systems. I helped design and build an X-ray telescope called USA (Unconventional Stellar Aspect X-ray telescope) that is now in low earth orbit and taking data. Such space based X-Ray timing instruments offer a powerful tool to experimentally probe such objects. I also was one of the originators of GLAST (Gamma-ray Large Area Space Telescope), which started development in 1992. In the context of a large collaboration of scientists from around the world, I am helping to design and build this instrument. I hope to use GLAST to help discover the nature of dark matter.

Dark Matter

For years the scientific community believed that what astronomers saw through their telescope lenses was all that made up the universe: there was nothing else. But in the mid-1900s this idea was challenged through the introduction of a new idea, called dark matter. Today this is a widely accepted idea and much research has and is going on in an attempt to define it. As implied by its name, dark matter can not be "seen" with our telescopes here on Earth. This is because it does not emit or absorb light, making it extremely difficult to detect. This explains why it has taken us so long to discover it. On account of this we are only able to "observe" dark matter by its effects on the matter around it. For example the larger the mass of an object, the greater its gravity, and the greater its gravity the more it can effect objects around it.

Though we still do not have a concrete idea of what makes up dark matter, most of the scientific community believes that dark matter falls into one of two groups, the MACHOS (massive compact halo objects) and the WIMPS (weakly interacting massive particles) MACHOS (massive compact halo objects) are what we call "normal" matter and are things like brown dwarf stars and massive planets. Brown dwarf stars aren't massive enough to start nuclear burning and become luminous. If Jupiter was about ten times heavier, it would be massive enough to start nuclear burning and would be a small star instead of a massive planet. The term WIMPS (weakly interacting massive particles) also called exotic matter, refers to anything that is not an electron, proton, or neutron. These are heavy particles that only interact very weakly with other matter. Some examples are neutralinos and axions; neutrinos also fall into this category.

Despite all that we do know about dark matter there are still a lot of things that we don't know for instance:

What is the dark matter?

Is there more than one type of dark matter?

What roles did the dark matter and dark energy play in the formation of structure in the Universe?

What other fossil relic messengers from the early Universe are awaiting our discovery?

Does the dark matter content change as we look back in time?

Perhaps one day we will know the answer to some of these questions. We are building GLAST in the hope that some of the high-energy gamma-rays we detect will help to shed some light on dark matter.