Date: September 11th, 2012

Title: A New Dark Energy Experiment

Podcaster: Rob Sparks and Arjun Dey

Organization: NOAO


Description: One of the biggest puzzles in astronomy and physics is the mysterious substance called dark energy which is causing the expansion of the universe to accelerate. In this podcast, NOAO’s Arjun Dey talks about a proposed instrument for the Mayall 4 meter telescope called BIGBOSS. BIGBOSS is a 5,000 fiber spectrograph that will attempt to help solve the puzzle that is dark energy.

Bio: Rob Sparks is a science education specialist in the EPO group at NOAO and works on the Galileoscope project (, providing design, dissemination and professional development. He also pens a great blog at

Arjun Dey is an NOAO Project Scientist for BIGBOSS. He earned his PHD from the University of California-Berkeley. His research interests are galaxy evolution, high redshift galaxies and large scale structure.

Today’s Sponsor: This episode of the 365 Days of Astronomy podcast is sponsored by the National Optical Astronomy Observatory. NOAO is a US national research and development center for ground-based nighttime astronomy. We provide astronomers access to world-class observing facilities on a peer-reviewed basis. Our mission is to engage in programs to develop the next generation of telescopes, instruments, and software tools necessary to enable exploration and investigation through the observable Universe. For information on observing proposals or our public programs, please visit for more information.

Additional sponsorship for this episode of 365 days of astronomy was provided by – Expanding your horizons in astronomy today. The premier on-demand telescope network, at dark sky sites in Spain, New Mexico and Siding Spring, Australia.

Rob: Hi, this is Rob Sparks of the National Optical Astronomy Observatory. I would like to welcome you to his episode of the 365 Days of Astronomy Podcast. I am here this morning with Arjun Dey of NOAO. Good morning, Arjun.
Arjun: Good morning.

Rob: How are you this morning?
Arjun: It’s great to be here.

Rob: First could you tell us a little about your academic background, your research and what your role is here at NOAO.
Arjun: Sure, I am a staff astronomer here at NOAO. I studied astronomy at the University of California-Berkeley where I got my PHD and before that I was an undergraduate at Northwestern University. After I finished my degree I was a post-doc at both NOAO and Johns Hopkins University and now I am back here as a staff member.

Rob: Coming home again, huh?
Arjun: Yes, love being in the desert.

Rob: We are here today to talk about a future project which hopefully will come to fruition in the next few years here called BIGBOSS which is a prop0sed instrument for the Mayall 4 meter telescope on Kitt Peak. Could you tell us what is BIGBOSS?
Arjun: BIGBOSS is a very ambitious project. You may have heard last year with the Nobel Prizes being awarded in physics to three researchers who discovered not only is the universe expanding but that the expansion is actually accelerating. It turns out that we now know that everything that makes us up, the atoms and the molecules, constitute about 5% of the energy density of the universe and 95% of the energy density of the universe is completely unknown. It’s something that we call dark matter, that’s about another 25% of it, and the remaining 70% or so is something called dark energy that we know almost nothing about. So BIGBOSS is an instrument and a project, it’s a project to build a very wide field highly multiplexed spectrograph for the four meter Mayall telescope on Kitt Peak. It will allow us to take spectra of 5,000 objects in the sky, stars or galaxies, all simultaneously. So it’s really a huge advance in our ability to map the universe. And this project is going to try and measure ripples in the matter distribution of the universe. In the very early universe, which acts sort of as a big plasma if you will, sound waves travel out like little ripples in a pond when you drop a stone in. At some point they are frozen into the distribution of matter in the universe. What we are trying to measure in the galaxies is the ripple, this ripple pattern in space. Using that ripple pattern we try to measure the expansion rate of the universe and that tells us how the universe has expanded over the last 8-10 billion years of its history.

Rob: So an imprint from the universe’s past.
Arjun: That’s right. Its basically an echo, if you will, of the sounds the universe used to make in the past. We are going to be mapping that over a huge range, a huge fraction of the history of the universe.

Rob: This project is actually a follow on to a project called BOSS, I believe. What happened with BOSS?
Arjun: BOSS was indeed a pathfinder project for BIGBOSS. It is currently underway on the Sloan telescope in New Mexico. The Sloan telescope is a 2.5 meter telescope and BIGBOSS represents about a factor of 10 increase in the ability to get redshifts of faint galaxies. The Mayall telescope is a four meter telescope so it’s a much larger telescope than the Sloan telescope. Plus the area that we will cover with the spectrograph is about three degrees with the new BIGBOSS, plus we will be able to get spectra of 5,000 galaxies at one time. So it’s a very big advance over BOSS. BIGBOSS will map a larger area of sky than the BOSS project. It will also survey the universe further back in time than the BOSS project was able to because we have a bigger telescope and are able to observe fainter and more distant galaxies. So it’s a significant increase in terms of its scientific reach and also we will be studying this mysterious dark energy at exactly the epoch when it began to kick in its power to accelerate the expansion of the universe.

Rob: You are going to be using this instrument to look at the imprint of sound waves from the early universe so what does this tell us? What are the science goals of BIGBOSS?
Arjun: The main science goal is to study how the expansion of the universe has changed over time. And knowing how it changed with time tells us something about what may have been driving it. There are many theories out there about what is powering this change in the expansion rate and knowing how the expansion rate changes allows us to discriminate between different theories. We have a very poor understanding at the moment of what the dark energy is and I think we are really a long ways from understanding its origins and its ramifications. However, we are very much at an exploratory stage and learning about how the universe was expanding and the rate at which it was expanding in the past tell us a lot about how to discriminate between these theories.

Rob: So what is the time frame for building BIGBOSS? How long do we have to wait to start getting results from this instrument?
Arjun: Well, we are in the process of designing the instrument now and finalizing the design. If the funding all comes through we hope to be commissioning the instrument sometime at the end of 2017 or 2018. That would be he timeframe when we would first start getting data with the instrument. The project would then run for a period of about three to five years so we would probably finish about 2021 or so. It will be the first time we have a good idea of how the expansion rate changed from a time in the universe about 10 billion years ago to about 7 or 6 billion years ago.

Rob: And this is a joint project with the Department of Energy, correct?
Arjun: That’s right. It’s actually an international project. A significant fraction of the funding, about half, we hope, is going to come from the Department of Energy. There are also international partners, various universities in France, Spain, China and Korea all involved in this project. They have all made commitments but everyone is waiting for the project to be authorized by the Department of Energy and the National Science Foundation.

Rob: Well, that sounds like very exciting future project to come to Kitt Peak.
Arjun: That’s right. It sort of continues our tradition at the National Observatory of supporting dark energy research. As you know the discovery of the acceleration of the universe was made in large part by our telescopes in Chile and by various calibration observations made at Kitt Peak and this sort of continues that tradition of us trying to understand the origins of the universe.

Rob: Well, I look forward to this instrument being built and coming into service on Kitt Peak in the next 5-7 years here and thank you for joining me today.
Arjun: I look forward to it too. Thanks very much. This was fun.

Rob: Thanks. This is Rob Sparks for the 365 Days of Astronomy Podcast and I hope you will join us for next month’s episode.
End of podcast:

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