sign in sign up
<<
Home , Alex Filippenko, Marc Aaronson, Mario Hamuy

Journal and Proceedings of the Royal Society of New South Wales, vol. 144, nos. 3&4, pp. 83-90. ISSN 0035-9173/11/020083-8

The accelerating

A new view of the universe

Ragbir Bhathal

School of Engineering, University of Western Sydney, Kingswood Campus, Penrith, NSW 1797

Email: [email protected]

Abstract

Brian Schmidt was the leader of one of the two search teams that discovered the universe is accelerating. His discovery was named Science Magazine’s breakthrough of the year for 1998 and in 2011 he was awarded the Nobel Prize for , along with Saul Perlmutter (University of California, Berkeley) and (John Hopkins University). He is a Fellow of the Australian Academy of Science and of the US National Academy of Sciences. He has made significant contributions in observational , supernovae, gamma ray bursts and all-sky surveys. This paper is based on an interview with him. It traces the trajectory that led to the accelerating universe and other achievements in .

Keywords: accelerating universe, , , Hubble constant, supernovae.

Introduction parents. From his father, a fisheries biologist he saw “the whole academic stream From Missoula, Montana to Alaska, to Arizona, to Boston to Australia and the accelerating and it quite appealed to me”, he said. He also universe! Incredible as it sounds this is the long, learnt the basic scientific skills of observation arduous and exciting journey that Schmidt and experiment from him. “My mother”, he travelled over the first thirty-one years of his life. said, “did a Master’s degree in social sciences It was a life full of ups and downs. As a young and I guess she showed me that there is a bunch boy he had already got a taste of moving from of skills that she used in her jobs which are one place to another as his parents followed important as a scientist, which I think has made their careers and academic pursuits. So this me a better scientist than I would have been movement from one place to another was otherwise”. It is perhaps his mother’s influence inbuilt into his psyche. In some ways it was a that has made him an excellent communicator traumatic experience for a growing lad but he of scientific ideas and an interesting and lively seemed to have taken the changes in his stride speaker for astronomy and science. as he made new friends and lost old ones and acclimatised himself to new places and He did not attend posh private schools but environments. spent his entire school life in government

schools which in some cases had very good and Born in the small country town of Missoula, highly motivated teachers. When he was Montana in the Rockies in the northern part of fourteen his parents moved to Alaska. He the , he was very close to his young attended Bartlett High School which according upwardly-mobile parents. As a young boy he to Schmidt, “was a superb school. The teachers acquired the protestant work ethic from his there were funded by Alaskan oil money and so

JOURNAL AND PROCEEDINGS OF THE ROYAL SOCIETY OF NEW SOUTH WALES 83 Bhathal – The accelerating universe…

I had four teachers that had PhDs at high White, Rob Kennicutt, Dave Arnett, Craig school and, you know, going to university was Hogan, Jim Leibert, and Frank Low. Leibert quite a step down and that’s extremely unusual”. was working on white dwarfs while Low was He came under the influence of some very good carrying out his well known studies in science teachers who challenged him. But they astronomy. were a little concerned that he wanted to do physics because many of their best students On completing his undergraduate degree he had went out and failed physics. “And their view to decide where to go for his PhD studies. He was that I wasn’t the best they ever seen and I could have gone to the University of California was going to fail. I think I probably surprised Santa Cruz where Sandy Faber, Mike Bolte, Stan them how well I did”. Woosley, George Blumenthal, Peter Bodenheimer and David Koo were extremely From Arizona to Harvard active in studies that interested him but instead he chose to go Harvard University where From Alaska he went to the University of Robert (Bob) Kirshner was actively engaged in Arizona in Tucson to do his undergraduate research on supernovae. His decision to go to studies. Why to Arizona, when he could have Harvard was made when he attended the first gone to the University of Washington which Marc Aaronson Memorial Lecture given by was closer to home or the University of Kirshner at the . Marc California? The University of California, he Aaronson (a close collaborator of Jeremy said, “was too expensive and hard to get into”. Mould, a former Director of the Mount Stromlo He is not sure why he chose Arizona. “And to Observatory and now of the National Optical this day, I still ask myself, why did I go to the Astronomy Observatory in Tucson) was killed University of Arizona?” Although at the time in a freak telescope accident. According to he applied to study at the University of Arizona, Schmidt, he said to Kirshner, “I’ll make you a he was not aware of the poor reputation of the deal. You let me be your student, allow me to Physics Department. However, he was aware work on supernovae and I’ll come to Harvard that the astronomy department had a good because I have to make a decision. He replied, reputation. After all Bart Bok (a former “Okay it sounds good”. Once there he was not Director of the Mount Stromlo Observatory in very keen on the supernova topics that Kirshner Canberra) was an excellent representative of the was suggesting. So he came up with his own astronomy department at that University. He idea for his PhD thesis. He informed Kirshner spent most of his undergraduate years working that he would like to measure the Hubble long hours on his studies. “Spending almost constant using supernovae, not just any sixty to seventy hours a week working on his supernovae but SN II. Unlike Supernovae Ia studies”, he said. Apart from the physics which are thermonuclear explosions in white classes, he attended “a lot of astronomy classes dwarfs, type II supernovae result from the and I had a good teacher there. Thomas collapse of a massive star. When the outside of Swihart”. The academic staff were supportive a SN II is ejected, it is still mostly hydrogen. and according to him, “they set me up to do a The properties of the expanding, cooling research project which I got embedded in with a atmosphere can be computed in detail and this guy by the name of John McGraw and was done by Ron Eastman, a postgraduate interestingly enough, one of the things I got student in Kirshner’s group (Eastman & involved in doing was looking for supernovae”. Kirshner 1989). By repeated measurements of Some of the at the time he was the temperature, speed, and brightness of the there he recalls were Peter Strittmatter, Simon

JOURNAL AND PROCEEDINGS OF THE ROYAL SOCIETY OF NEW SOUTH WALES 84 Bhathal – The accelerating universe… supernova atmosphere it is possible to figure 1990s. According to Schmidt, “there was the out how large the atmosphere is and compute Sandage, et al. group who were convinced it was the distance to the explosion. Schmidt teamed 50. There was the Mould, et al group who up with Eastman who was “writing a very fancy thought it was 80 something but were not quite computer code” which modelled what was sure”. Schmidt started out with a value of 60 happening in the supernova from a physical but “then we re-did the models and made some basis. “I worked with Ron Eastman and Bob improvements and it drifted to 73. So at 60 I very carefully to model these supernovae and was very popular with Alan Sandage. At 73 he that told us how many watts they put out so that called me a traitor. I think he has forgiven me”. we could therefore know how bright they appeared on Earth, compare that to how many Schmidt’s PhD thesis was significant and it watts intrinsically they were, and using the provided confirmation of the Key Project inverse square law, the fact that light gets fainter team’s measurements of the Hubble constant by distance squared, measure the distance with the of 72 directly to objects outside of the local universe”. kilometres per second per megaparsec. The key Using the expanding photosphere method he project work was mostly carried out by Jeremy measured fourteen supernovae for his PhD Mould and Brad Gibson at Mount Stromlo thesis. This enabled him, “to measure a value of Observatory. Other key players were Wendy the Hubble constant which was independent of Freedman at Carnegie and Rob Kennicutt at the any other means and could be compared University of Arizona (Freedman et al. (2001)). directly with cepheids and it turns out the value According to Schmidt the work he did on the I got, 73 plus or minus eight kilometres per Hubble constant “was a good grounding in second per megaparsec” was very close to the what came later, the accelerating universe”. now accepted value of about 72 km/s/Mpc (Schmidt B et al. (1994)). It is interesting to It was unusual to be given an internal job note that some of the with SN II data straight after a PhD at Harvard but that was and expanding photosphere distances were also exactly what happened in the case of Schmidt galaxies in ’s Key Project when he finished his PhD in 1993. According sample. The results agreed very well. to Kirshner, “Although we usually liked to push the fledglings out of the nest, Brian was so At the time he was doing his work on extraordinary he won one of the competitive supernovae II there were two other groups who postdoc jobs at the Centre for . were also measuring the Hubble constant (H0). This gave him the chance to step out as an There was controversy and acrimonious debate independent worker” (Kirshner 2002). as to what was the real value. In the 1970s Gerard de Vaucouleurs then at the University of To Australia and the accelerating Texas and a past member of the academic staff of Mount Stromlo Observatory favoured a high universe value for H0, of around 80 or 90 while Alan On a visit to Harvard, Mario Hamuy from Chile Sandage and Gustav Tammann strongly not only showed Schmidt and his colleagues maintained that 50 was the correct answer. new supernova data but also showed them Sandage, a protégé of Hubble (Overbye (1991)) “very clearly you could use Type Ia supernovae believed that he owned H0 and anyone who did to measure accurate distances”. According to not accept this value was an idiot or a country Schmidt, “In 1991, there was the idea that Type bumpkin. The debate dragged on into the Ia supernovae were perfect standard candles. I

JOURNAL AND PROCEEDINGS OF THE ROYAL SOCIETY OF NEW SOUTH WALES 85 Bhathal – The accelerating universe… was very sceptical about using Type Ia objects to enable them to trace back the supernova for cosmology because we didn’t expansion history of the universe. They had know very much about them”. In 1991 two begun a serious study of supernovae in the late unusual supernovae, SN 1991T and SN 1991bg 1980s with a combination of Rich Muller from were discovered. They strengthened the case the Physics Department and the Lawrence that there were real differences among SN Ia Berkeley Laboratory, including Carl and their discovery cast doubt as to whether SN Pennypacker (Filippenko et al. (2001)). Alex Ia could be used as standard candles Filippenko from the Astronomy Department (Leibundgut et al. (1993)). Supernova 1991bg joined them sometime in 1994. Perlmutter, with was intrinsically faint and appeared to be ten a forceful personality joined them later and times fainter than an earlier SN Ia in the same became the leader of the group although he was . It rose and fell much more quickly. On quite a junior academic. Schmidt’s view was the other hand SN 1991T was exactly the that “if those guys at Berkley can find opposite, it was much brighter and it rose and supernovae, we sure as hell can. We had all the fell more slowly. This intrigued Mark Phillips supernovae expertise, let’s get out and do that”. and by plotting the luminosity of several That was the genesis of the High-Z Supernova supernovae he found that the rate supernovae Team. It was formed at about the time Schmidt rise and fall is a very good indicator of how arrived in Australia at the Mount Stromlo bright they are intrinsically (Phillips (1993)). Observatory. He was twenty-seven years old. It According to Schmidt, “that was the is rather remarkable that he was going to lead an relationship with a new, independent dataset international team to explore the past history that was shown to me in 1994. They found that and the future of the universe at that young age. Phillips’ relationship made the supernova He said, “I knew I wanted to go back and behave very nicely, you can measure distances to measure the past history of the universe, but this about eight per cent in accuracy which may not was going to require telescope time which I did sound brilliant on Earth, but in astronomical not have access to in Australia”. He worked out terms when we are used to everything being a strategy to unveil the secrets of the universe. about thirty per cent, that was good. Eight per “We needed the world’s largest telescope, the cent was outstanding”. Mario Hamuy had taken Keck telescopes, we needed access to the Phillips idea and turned it into a solution to the Hubble Space Telescope. We needed a big puzzling luminosity differences in the whack of time on the wide field imager on the supernovae in a paper of which he was the first Cerro Tololo four metre. And so I went author (Hamuy et al. (1996)). In fact, he through and I took the people I knew in showed that Phillips was correct. The slow supernovae which was the Chileans, who helped declining supernovae are the bright ones and the determine the relationship that allows us to use fast decliners are the faint ones. By measuring them. Alex Filippenko from Perlmutter’s group how fast a fades after it at Berkeley joined us in 1995 when the power of reaches maximum brightness, you were not the Keck telescope became apparent. likely to make any mistakes in assigning it the Filippenko had access to Keck. Chris Stubbs, wrong distance. The scene was set for using who worked on the MACHO experiments here Type Ia supernovae as distance indicators. and was someone who was interested in large data sets was invited. Bob Kirshner, my In the same month Schmidt had found out that supervisor for his general expertise and Bruno Saul Perlmutter and his group at the University Leibundgut who had access to European of California, Berkley had found seven distant

JOURNAL AND PROCEEDINGS OF THE ROYAL SOCIETY OF NEW SOUTH WALES 86 Bhathal – The accelerating universe… facilities”. They started with about fourteen Anyway, the important thing is that the two people which eventually became twenty. groups were independent”.

In 1995 they found their first supernova – called It was a remarkable discovery. It was all the Supernova 1995 K which turned out to be an more remarkable because although there was extremely interesting supernova. The not much love lost between the two groups supernova was 40% fainter than he had when they first began on this quest they ended expected it. “This single object seemed to show up by agreeing that the universe is accelerating. that the universe is speeding up”, he said. But The discovery was Science Magazine’s discovery to provide concrete evidence they needed more of the year for 1998. Einstein’s blunder was not objects. a blunder after all. One recalls that earlier in the 20th century Einstein had added a cosmological 1998 was Schmidt’s year. It began with constant to his general theory of relativity to publishing a number of papers which tackled balance the motion of the universe so that it the problem of the state of the universe, would be stationary. So, I asked Schmidt experimental techniques to study the universe whether his accelerating universe confirms and the equation of state of the universe Einstein’s theory? According to Schmidt, “In (Garnavich et al. (1998a), Garnavich et al. some sense it does. I’m not sure whether it (1998b), Riess (1998), Schmidt et al. (1998)). confirms it but it certainly is pointing towards “At the end of 1997, Peter Garnavich had put the . But it is hard to together four new objects (five in total) now, understand why the cosmological constant is so and these showed that the universe was not small and not zero”. slowing down quickly. It was a month later when Adam Riess (along with Schmidt and Supernovae provide the only evidence for Garnavich – who were the three postdocs in the acceleration but when combined with the group) assembled fourteen objects that we saw microwave background an interesting picture of the signal of acceleration”, Schmidt informed the universe emerges. The measurements me. So in 1998 they showed that the universe allowed the astronomers to pin down how wasn’t slowing down at all. Indeed, it seemed to much dark energy (Ωλ) and how much dark be speeding up. According to Schmidt, “It was matter (Ωm) the universe contains. The a big thing because here we have observations supernova data gave a value of Ωm – Ωλ and the that the universe is speeding up. What does it cosmic microwave background (CMB) mean? It means that the universe has to be full measurements gave a value of Ωm + Ωλ. So in of an energy which pushes on the universe their paper on the constraints in cosmological rather then pulling it. We were telling the world models the High-Z Supernova team crossed the that seventy per cent of the universe is made up data from supernova with that of the CMB of a material that you did not know existed. (Garnavich et al. (1998b), Tonry et al. (2003)) That is, there is something out there ripping the and to their amazement found Ωm = 0.3 and Ωλ universe apart which is the most fundamental = 0.7. In effect, the results were telling the thing in the universe and we never knew it astronomers that in the early universe the existed. And we did this with the Perlmutter density of matter in the universe was greater group who turned out had independently made than now and at some point in time dark energy the discovery. Our papers came out ahead of took over to give us an accelerating universe in theirs. They hit the press release before we did. which we live today. But the astronomers don’t

JOURNAL AND PROCEEDINGS OF THE ROYAL SOCIETY OF NEW SOUTH WALES 87 Bhathal – The accelerating universe… have a clue what the dark energy is that is on, and what age it did and the process behind accelerating the universe. it”. The objects could also be used as places to undertake radio observations with the Has the problem of the cosmological Murchison Widefield Array to look at the parameters been completely solved or were hydrogen before it was ionised – a project being there some other problems which needed to be worked on by a range of astronomers across resolved, I asked Schmidt. According to him, Australia, and the US at MIT and Harvard. He “I’m fairly heretical on this. And I believe we’ve hopes to feed objects for them to look at. done most of it. The theorists are aching to show that it isn’t the cosmological constant. My Another interesting thing he said, “we can do is view is we’ve shown that it’s close to the to look at the first stars in our galaxy. We can cosmological constant. And I think we can actually pinpoint the stars that have almost probably improve things by a factor of three nothing other than hydrogen and helium in with $1 billion. That’s where we are at. A them by their colours. And right now this billion dollars gives you a factor of three university (i.e., the Australian National improvement in our measurement. And if the University) is leading this area of research”. billion dollars do not show anything, that’s a very expensive billion dollars for not a lot of The Oort Cloud which was first postulated by gain. So that is where we are heading, the Dutch Oort will also come measuring the equation of state. But it’s not under his scrutiny. It is the home of comets. something that interests me. I’m doing it as a “Paul Francis will be using the SkyMapper to sideline, but I’m trying to shift my focus to find out what’s going on in the Oort Cloud by other things because I think we have done most seeing what is going on in the outer solar system of what we can do and it’s time to move on to with these comets as they come into our other problems which are more interesting”. neighbourhood”. He sees the SkyMapper as a great resource “not just for me, but for the Skymapper entire astronomical community”. As we roamed over a number of astronomical topics He is the team leader of the SkyMapper project and drank several cups of coffee, I finally asked (http://www.mso.anu.edu.au/skymapper) Schmidt what he considered was the major which will be constructing a comprehensive achievement in his life to date? “Certainly the digital map of the southern sky. He said, “It will accelerating universe is a level above everything produce a petabyte of data. It will be used to else I have done and probably will ever do. It is find very rare objects and help us answer a my hope that SkyMapper will come close to the whole range of different science issues”. So accelerating universe. It will not reach the what were the issues he was trying to solve. novelty of the accelerating universe but my According to him, “There are a few intrinsically hope is it will be a major iconic piece of work at bright, but not too bright quasars that were that level. The work we have done in gamma formed at the dawn of the first stars. And there ray bursts has been good. The work on are three known right now from the northern supernova physics and the Hubble constant was hemisphere search which did not go as far as actually quite an influential piece of work”. the SkyMapper will go and has not done as Perhaps, we will hear of more major discoveries much sky area. And so, we should be able to with the SkyMapper in future years. take those three objects and make twelve or fifteen. And those objects will allow us to probe the universe and see how the universe turned

JOURNAL AND PROCEEDINGS OF THE ROYAL SOCIETY OF NEW SOUTH WALES 88 Bhathal – The accelerating universe…

Conclusion M. (1998a) Supernova limits on the cosmic equation of state; Astrophysical Journal; 509, 74-79. This paper has shown some aspects of the life Garnavich, P. M., Kirshner, R. P., Challis, P., and scientific achievements of one of Australia’s Tonry, J.; Gilliland, R. L., Smith, R. C., foremost astronomers. It has revealed the steps Clocchiatti, A., Diercks, A., Filippenko, A. V., that led to the discovery that the universe is Hamuy, M.,Hogan, C. J.,Leibundgut,B., Phillips, M. accelerating and the amount of dark matter and M., Riess, A. G., Schmidt, B. P., Schommer, R. A., dark energy the universe contains. Spyromilio, J., Stubbs, C., Suntzeff, N. B. and Wells, L. (1998b) Constraints on the cosmological models from the Hubble Space Telescope Acknowledgements observations of High-Z supernovae; Astrophysical The author thanks Professor Brian Schmidt, Dr Journal Letters; 493, L53. John Davids and an anonymous reviewer for Hamuy, M., Phillips, M. M., Suntzeff, N. B., Schommer, R. A., Maza, J. and Aviles, R. (1996) reviewing and providing useful comments on The absolute luminosities of the Calan/Tololo the paper. The author also thanks the National Type IA supernovae; Astronomical Journal; 112, 2391- Library of Australia for sponsoring the National 2397. Oral History Project on significant Australian http://www.mso.anu.edu.au/skymapper Astronomers and Physicists. The interview with Kirshner, R. P. (2002) The extravagant universe, Professor Brian Schmidt was conducted in 2006 Princeton University Press, Princeton, USA. at the Mount Stromlo Observatory (now known Leibundgut, B., Kirshner, R. P., Phillips, M. M., as the Research School for Astronomy and Wells, L. A., Suntzeff, N. B., Hamuy, M., Astrophysics) in Canberra. The full transcript Schommer, R. A., Walker, A. R., Gonzalez, L., of the interview is held in the Oral History Ugarte, P., Williams, R. E., Williger, G., Gomez, M., Marzke, R., Schmidt, B. P., Whitney, B., Collections of the National Library of Australia. Coldwell, N., Peters, J., Chafee, F. H., Foltz, C. B., References Rehner, D., Siciliano, L., Barnes, T. G., Cheng, K. P., Hintzen, P. M. N., Kim, Y. C., Maza, J., Parker, Eastman, R. G. and Kirshner, R. P. (1989) Model J. Wm., Porter, A. C., Schmidtke, P. C. and atmospheres for SN 1987a and the distance to the Sonneborn, G. (1993) SN1991bg – A new of Type Large Magellanic Cloud; Astrophysical Journal; 347, IA supernova with a difference; Astronomical 771-793. Journal; 105, 301-313. Filippenko, A. V. (2001) Einstein’s biggest blunder? Overbye, D. (1991) Lonely hearts of the cosmos, Pan High- supernovae and the accelerating Books Limited, London, UK. universe; Publications of the Astronomical Society of the Phillips, M. M. (1993) The absolute magnitudes of Pacific; 113, 1441-1448. Type IA supernovae; Astrophysical Journal; 413, Freedman, W. L., Madore, B. F., Gibson, B. K., L105-108. Ferrarese, L., Kelson, D. D., Sakai, S., Mould, J. R., Riess A G (1998) Observational evidence from Kennicutt, R. C. Jr., Ford, H. C., Graham, J. A., supernovae for an accelerating universe and a Huchra, J. P., Hughes, S. M. G., Illingworth, G. D., cosmological constant; Astronomical Journal; 116, Macri, L. M. and Stetson, P. B. (2001) Final results 1009-1038. from the Hubble Space Telescope Key Project to Schmidt, B. P., Kirshner, R. P., Eastman, R. G., measure the Hubble Constant; Astrophysical Journal; Phillips, M. M., Suntzeff, N. B., Hamuy, M., 553, 47-72. Maza, J. and Aviles, R. (1994) The distances to five Garnavich, P. M., Jha,S., Challis, P., Clocchiatti, A., Type II supernovae using the expanding Diercks, A., Filippenko, A. V., Gilliland, R. L., photosphere method, and the value of H ; Hogan, C. J., Kirshner, R. P., Leibundgut, B., o Astrophysical Journal; 432, 42- 48. Phillips, M. M., Riess, D., Riess, A. G., Schmidt, B. Schmidt, B. P., Suntzeff, N. B., Phillips, M. M., P., Schommer, R. A., Smith, R. C., Spyromilio, J., Schommer, R. A., Clocchiatti, A., Kirshner, R. P., Stubbs, C., Suntzeff, N. B., Tonry, J. and Carroll, S. Garnavich, P., Challis, P., Leibundgut, B.,

JOURNAL AND PROCEEDINGS OF THE ROYAL SOCIETY OF NEW SOUTH WALES 89 Bhathal – The accelerating universe…

Spyromilio, J.,Riess, A. G., Filippenko, A. V., Holland, S., Jha, S., Kirshner, R. P., Krisciunas, K., Hamuy, M., Smith, R. C., Hogan, C., Stubbs, C., Leibundgut, B., Li, W., Matheson,T., Phillips, M. Diercks, A., Reiss, D., Gilliland, R., Tonry, J., Maza, M., Riess, A. G., Schommer, R., Smith, R. C., J., Dressler, A., Walsh, J. and Ciardullo, R. Sollerman, J., Spyromilio, J., Stubbs, C. W. and (1998) The High-Z Supernova Search: Measuring Suntzeff, N. B. (2003) Cosmological results from cosmic deceleration and global curvature of the High-Z supernovae; Astrophysical Journal; 594, 1-24. universe using Type 1A supernovae; Astrophysical Journal; 507, 46-63. Tonry, J. L., Schmidt, B. P., Barris, B., Candia, P., Challis, P., Clocchiatti, A., Coil, A. L., Filippenko, A. V., Garnavich, P., Hogan, C.,

Ragbir Bhathal PhD

(Manuscript received 9 August 2011; accepted 26 October 2011.)

Dr Ragbir Bhathal was President of the Royal Society of NSW in 1984 and was awarded the Royal Society of NSW Medal in 1988. He has published several papers in international refereed journals and fifteen books, eight on astronomy.

JOURNAL AND PROCEEDINGS OF THE ROYAL SOCIETY OF NEW SOUTH WALES 90