Thursday, October 25, 2012

The Nearest Exoplanet Discovered. Probably.

The astronomy news last week was dominated by one story: a planet may have been discovered around the Sun-like star Alpha Centauri B, as reported in Nature. This is exceptional because, if confirmed, it will be the nearest exoplanet to the Earth. The mass of this exoplanet candidate is about the same as the Earth, which would make it the lightest exoplanet ever found around a star like the Sun. This is an exciting result.

An artist's impression of the planet around Alpha Centauri B. Credit: ESO/L. Cal├žada/Nick Risinger (skysurvey.org)
The details of the astrophysics have been well described by many different authors, including several that I cite below. Instead of covering this well-trodden ground, I'll discuss how the result was communicated to the public, including the issue of expressing uncertainty in describing new results. I'll also mention the embargo break that presented some challenges for those doing the publicity and for science writers.

Did you notice how carefully I worded the description of this result? I used "may", "if confirmed" and "planet candidate". The exoplanet candidate has not been observed directly. Its existence is inferred from the tiny, rhythmic wobble apparently seen in the star Alpha Centauri B, after several, much stronger signals have been subtracted away. No other team has reported evidence for planets in the Alpha Centauri system, and if they had, this new paper wouldn't be such big news.

I've read the paper and I think there's a good chance that a planet has been found, but I think confirmation is needed (the reader might ask how I even have a clue about this: see a footnote [1] for a brief explanation). I'm not the only person who thinks this. Artie Hatzes, an astronomer from Thuringian State Observatory, in Tautenburg, Germany wrote a News and Views article for Nature where he expressed similar views. He uses words like "possible extrasolar planet", and "if it is confirmed" and uses the phrase "candidate exoplanet" four times. He also uses the "extraordinary claims require extraordinary evidence" line, from Carl Sagan and says that although a "planet-like" signal is found, the "discovery does not quite provide the "extraordinary evidence"".

Another planet expert, Debra Fischer, agrees that confirmation is needed. In a Planetary Society interview with Bruce Betts, she compliments the authors of the Nature paper for their new analysis techniques, but says: "Nevertheless, because these corrections essentially constitute a new approach, confirmation is critical."

All of the science writers on Nature's embargo list were sent a copy of the News and Views article in advance. So, most of them would have been aware of Hatzes' reservations. How much of this doubt made it into the media coverage of this paper? A good amount of it did. Dan Vergano from USA Today wrote one of the more carefully worded articles beginning with this summary:
"Our nearest star-system neighbor, Alpha Centauri, may have an Earth-sized planet orbiting one of its three stars. If confirmed, the planet orbits too close to the star for life." 
He then quoted Artie Hatzes' caution later in the article. Vergano later says
"Dumusque says that more looks at the star should strengthen the finding and notes that there is a possibility that the planet may slightly eclipse, or transit, in front of the star, another tell-tale sign of its existence measurable by astronomers." 
So, not only does Vergano mention that the finding needs to be strengthened, he discusses ways to confirm the result. Nicely done.

Nadia Drake, writing at Science News includes a good quote from Debra Fischer: "It's a tough detection, there's absolutely no question about it," Fischer says. "A detection that's as technically difficult as this one requires confirmation." Drake then segues into an excellent, detailed discussion of plans to confirm the result.

John Timmer, writing for Ars Technica, gave a good, detailed explanation of the technique used by the planet hunters, as they eliminated other signals until a "a hint of a signal with a periodicity of 3.3 days" was left. His statement that "it's probably a planet" (his emphasis) rings true.

Brian Vastag from the Washington Post quoted Artie Hatzes about the need for confirmation by other teams. Dennis Overbye, from the New York Times, wrote that astronomers were electrified by the news of the planet but they also cautioned that it needed to be confirmed by other astronomers. I was interested in seeing more here, but he doesn't give any details about the doubts or the astronomers who expressed them, because he goes on to quote Debra Fischer saying it's the story of the decade. Maybe there was an overzealous editor at work here.

Phil Plait, at his Discover Magazine blog "Bad Astronomy" wrote an extremely enthusiastic description of the result along with an impressive level of technical detail and some science fiction perspective. He doesn't provide any obvious qualifiers, but he's an experienced astronomer so this can be considered an opinion piece as well as a report. He read the paper and found it "pretty convincing".

Other writers also decided not to include qualifiers about the result, or had editors remove them. Instead of calling these out, I'll give a few possible explanations for these omissions. First, the authors addressed concerns about the significance of the result on a press conference held by ESO. The first question was from Seth Borenstein, of the Associated Press, who asked
"Can you address Hatzes' issue in his N&V that this an extraordinary claim and if you follow Sagan's rule, it requires extraordinary proof and he doesn't think this is enough". 
One of the authors answered by saying that they estimated there's a 1 in 1000 5000 chance that this is a "false-alarm". Other writers asked questions about seeking confirmation.

Second, the paper itself does not use qualifiers. For example, the abstract includes: "Here we report the detection of an Earth-mass planet orbiting our neighbour star Alpha Centauri B". Presumably, most or all of the authors of the paper along with the two or three referees agreed that qualifiers weren't necessary. So, adopting the view that peer-reviewed papers can offer a useful approximation of The Truth, one can argue that qualifiers were not essential for a press report.

Third, there was no shortage of exoplanet experts who were very excited about the result and who weren't expressing doubts, at least in quotes made public. This includes people like Geoff Marcy, Alan Boss and Sara Seager. Science writer Ross Andersen, writing for the Atlantic, asked Sara Seager whether this is a candidate or if it has been confirmed, and she responded "To answer your second question, we consider this particular finding a detection. It's not a candidate; it doesn't need to be confirmed. It's a detection." What's going on here? It's not a shock to see scientists disagree about the credibility of a new result, especially if they have different backgrounds. In this case, Hatzes and Fischer are mainly observers, while Seager does more theory. It's possible that there are differences being used in the definition of key words like "detection" and "candidate", with the observers demanding a higher threshold for detection.

It's well known that people can have subtle biases that make it difficult to be objective, and scientists are not exempt from these problems. I won't attempt to speculate about other people's point-of-view, but I'll give you a personal example. Do I like Artie Hatzes' News and Views article because I'm convinced it's the most objective and carefully-considered reaction to this new result, or because he happened to give a very positive referee's report to an early paper of mine? I don't think it's the latter, but it's difficult to say I don't harbor *some* bias. I *will* openly admit my experience doing publicity and following others doing it is an issue for me, as I've seen results come and go or be seriously contested, some recently.

Other challenges for writers might be connected to any word limits they have. If you have described the basics of a result and only have a hundred words left, you might see a choice between describing the need for confirmation, which some might find boring, and talking about the exciting possibility of sending probes to Alpha Cen B, or even traveling there. Bloggers don't have word limits - as I'm reminding readers with this article - and so they can fit more details in. However, as Vergano's article shows, it's possible to be concise and conservative. Another issue for writers was likely a lack of time, exarcerbated by the shorter than usual embargo time given by Nature and eventual embargo break, as I describe in the next section.

The science media, especially the mainstream media, is good at describing the latest big discovery (spurred on by press releases produced by people like me, but that's a story for another blog post). However, this can give a distorted view of how science really works. As Andrew Revkin said in his very first blog post at dotearth:
"The strength of science lies in the trajectory of understanding more than in any single finding, and the most durable ideas emerge from conversation, not monologue." 
Although he's describing his motivation for starting a blog, his comment summarizes a larger goal of scientific research. In the case of Alpha Centauri Bb, one can ask what needs to be done to satisfy skeptics like Artie Hatzes and Debra Fischer about whether a planet has really been detected. One study doesn't do the job. The authors have already offered assistance by providing their velocity data so that people can check their analysis. In other words, different teams are being invited to check their work, and I'm very confident that multiple teams are taking up this offer. It's possible that a different team will find a weaker signal, but it's also possible that a similar strength signal or a stronger one will be seen.

I asked for comments from planet expert Dave Charbonneau who passed along, via email, what he told others:
"Yes, the analysis makes sense to me. The authors present a long list of items they need to worry about for their data, and how they correct for them. But their description of these makes sense, they have done what I would do, and (most importantly) they are releasing their data. You can bet that within hours many scientists around the world will analyze these data and attempt to confirm the signal, and we will know shortly the result. This is the strength of a really exciting field -- the correction timescale is short. But I have no worries here, although I too will be keen to analyze the data. Who wouldn't?"
This is about the difference between confidence and certainty. Charbonneau is confident that the planet has been detected but he's not certain, and he wants to find out for himself, not just rely upon what others say. It's also important for completely independent work to be performed. Debra Fischer and her team are doing their own observations, as outlined here. Others may have been observing it, including some of my fellow Australians.

Does Sagan's principle of "extraordinary claims require extraordinary evidence" really apply here? A less vague way of applying that requirement might be: is an unusually high statistical significance required for a result of unusually high public interest? I would assert that it isn't. But, when there's such widespread interest I think there's a greater need to explain potential concerns with reliability and the steps required for confirmation.

Given the challenges involved with this story and the other explanations given above, I think writers did their jobs well. However, I think that serious discussion of uncertainty and the need for confirmation can make the difference between a good story and a great story. Critics might say this talk is too nuanced for readers. Well, some of them want nuance, as Emily Willingham has recently
written.

As a late addition to this post, I just saw that astrophysicist Lawrence Krauss strikes an excellent, skeptical tone in this Newsweek article where he says: "That astronomers can deduce this kind of motion in a star four light years from us is so amazing, in fact, that we should be cautious about accepting the validity of the new claim, which was published in Nature last week, until it is confirmed using another independent set of observations. The observed signal is so small that it must be extracted from far bigger random jitter in the star’s light. Many of my colleagues have expressed skepticism on this point, but if we weren’t skeptical we wouldn’t be scientists." Well said! I'll repeat that this was Newsweek!

EMBARGO MISADVENTURES

There was one obvious misadventure with the publicity effort. To give some background, Nature sent their summary of the result, along with a copy of the paper and the News and Views article by Hatzes, to science writers who agreed to honor an embargo. This means the writers could talk to the authors and to experts to research their stories, but couldn't publish their articles until 1pm EDT on Wednesday, October 17th, on Nature's regular schedule. Nature normally sends their press package out the week before the paper is published, but in this case they sent their package out on Monday, October 15th. Apparently they do this for their best results. Presumably, their thinking is that the embargo only has to hold for two days.

This photograph shows a view of the Milky Way behind the dome of the ESO 3.6-metre telescope at La Silla in Chile, where the observations of Alpha Centauri B were performed. Alpha Centauri is visible towards the upper right of this photo. Credit: S. Brunier/ESO

To publicize the result, the outreach people at the European Southern Observatory (ESO) organized an embargoed press conference at 10am EDT on Tuesday, October 16th. To participate, writers had to agree to honor the embargo. As an aside, I have had one science writer recommend several times that NASA should do embargoed press conferences, to give writers more time to prepare their stories. I asked J.D. Harrington, a public affairs officer at NASA about their policy on embargoes and here is his emailed response:
"NASA stepped away from putting anything out under embargo almost two years ago.  The primary reason was that they no longer make sense in today's 24-hour news cycle coupled with the competitive nature of the media market (always wanting to be first).  We've have numerous problems supporting embargos with many being broken.  As such, we no longer support them.  We also pushed hard against the major journals to get them to stop, but as you know, they vehemently resist change..."
Getting back to the exoplanet story, I had already noticed some buzz about this result on Twitter, with several mentions of a *big* exoplanet result coming. Not surprisingly the ESO press conference was a big hit, with over 60 science writers calling in. By the end, writers had a LOT of information about the result, including ESO's press package and substantial quotes from the researchers, plus the package from Nature. Assuming that the embargo held, they now had a bit over 24 hours to finish their stories. The embargo didn't make it. As documented by Ivan Oransky at his excellent blog Embargo Watch a writer for a Croatian news site broke the embargo with a story time-stamped at 17:25. Assuming this is Central European Summer Time, that's 11:25am EDT, so not long after the press conference likely ended. According to Embargo Watch, the news then spread around Twitter until it reached astronomy blogger Daniel Fischer, who alerted ESO and the American Astronomical Society, who both alerted Nature. Nature then decided to officially lift the embargo later on Tuesday.

Nadia Drake explained some more details to me about what happened. Someone saw the story on the Croatian website and posted it to Facebook, then someone saw that and did a blog post, and then someone saw that and tweeted about it. Once it reached Twitter it bounced around and news inevitably got back to Nature about the embargo break, as mentioned above. With the embargo lifted, stories could be published straight away, and the rush was then on to get stories out quickly. Some writers, like Drake, were anticipating an embargo break, so they got their stories finished early, just in case and then monitored sites like Twitter to see if anything slipped out. You can see that most of the articles mentioned above were published on Tuesday, October 16th.

This is a good case study in observing the big effect that social media, especially Twitter, is having in communicating science. Excitement built up, while the embargo held, and then the embargo break was quickly reported, so writers could publish their stories. One might say that the social media buzz indirectly contributed to the embargo break, but that would be speculation. Afterwards, the many stories were quickly spread around, with the best ones being deservedly celebrated. All of this happened in just a few days, like a Dan Brown novel, and it was fun to watch.  However, the story of Alpha Centauri Bb is not yet over and many mysteries remain about the system.


[1.] My PhD thesis at the University of Sydney involved searching for oscillations on stars like the sun, including Alpha Centauri A & B. The technique involved radial velocity measurements just like these exoplanet hunters, so there's a lot of overlap, except I was looking for wobbles *in* the star and they are looking for wobbles *of* the star. Also, I was searching for lower amplitude variations on a much shorter timescale.


Friday, October 12, 2012

Tales of a ScienceOnline Novice

A few weeks ago I registered for the ScienceOnline2013 conference being held early next year in North Carolina. This meeting is an unconference, with moderators who lead discussions, rather than giving full presentations. It's also extremely popular, almost a phenomenon all by itself, with strong demand for a limited number of available spots.

This will be the first time I've attended this meeting, which started in 2007 as the N.C. Science Blogging Conference and has been held annually ever since. But, I've been working in publicity for the Chandra X-ray Observatory ever since April 2003, with much of our outreach being done online. So, why did I wait so long to attend a ScienceOnline meeting, when the 7th meeting is approaching? How did I secure a spot for this heavily oversubscribed conference?

Before working in publicity I did full-time research in astronomy and, when I broke away from a computer, I attended astronomy conferences, especially American Astronomical Society (AAS) meetings. When I started working in publicity a lot of things changed, but I still went to the same AAS meetings. Instead of focusing on science talks, I concentrated on press briefings and talking to Chandra users, since a major goal was, and still is, to find the most exciting new results and publicize them. I was comfortable in my astronomical world. Meanwhile, science blogging was in its infancy and Twitter hadn't even started yet.

I didn't notice the Science Online meetings when they began. I didn't hear about them from astronomers and I didn't hear about them from colleagues working in publicity. We also didn't get any suggestions from science writers to attend these meetings. I followed a few science blogs, including those of Phil Plait, the Bad Astronomer and Sean Carroll and colleagues at Cosmic Variance, but I don't recall them saying much about these meetings.

Eventually I did start to hear about them, but only indirectly. One big change for me was getting onto Twitter. My colleague Kim Kowal, who had set up Chandra's popular Twitter account, had raved about how useful it was, but I had resisted. Then two things happened: I finally got my ancient, failing cell phone upgraded to an iPhone and I found out that my *Dad* had joined Twitter. How much of a dinosaur was I? This was just before the AAS meeting in early January of this year, so I decided to join Twitter so I could do some reporting from the meeting. I also found Twitter to be great for using on my train commute.

After following a bunch of science writers on Twitter I heard a *lot* about ScienceOnline2012, held later in January. Even then I didn't immediately think that I should attend one of these meetings. Most of the discussion on Twitter and in blogs was very smart, but it sometimes gave the impression of an exclusive club dominated by writers, especially when people noted how hard it was to get into this wonderful meeting. Did I deserve to have this exceptional experience?  Did it matter that I didn't have many followers on Twitter and didn't have a personal blog? Were my nerd credentials sufficiently worthy? (*)

Then I noticed Bora Zivkovic, the "Blogfather" and one of the organizers of ScienceOnline, mention a wiki for people to suggest ideas for the 2013 meeting. This is part of the unconference experience, where people suggest ideas for sessions in advance and others add comments to give their support. As the July 1st deadline for the sessions approached, Bora started posting about it with increasing frequency, but I was busy at work and didn't summon the energy needed to research a useful idea. I also wondered about originality. I'd seen people mention how certain ideas had been covered in detail at previous ScienceOnline meetings and I wasn't prepared to check over the content of all six previous meetings. Maybe I'd try the following year. It's easy to make excuses.

At some stage I saw two videos about the meeting, one a set of quick interviews with people that gave a good feel for the meeting and the second one a brilliant music video by Carin Bondar that almost won me over on the spot. I recognized a bunch of people in the video just from their Twitter bio photos, or online videos. This seemed like the place to be.



I had been wanting to share more about what I had learned doing publicity, both with scientists and with science communicators, and I also wanted to learn from others. The next ScienceOnline meeting seemed to be a great way to do this, if I could only get into it. I thought if I suggested a session and moderated it I would be guaranteed a spot. On the night before the deadline, I looked at the wiki and saw an idea to discuss press releases not being vetted by scientists before being put out. I'd seen some discussion on Twitter about it and it was interesting, but it covered just one issue and couldn't explain all of the poor press releases we had seen over the previous few months. Only a few days earlier there had been a suggestion by a communications expert for publicity people to go on a "press release diet", where they use social media to release information and phase out the traditional press release. So, I thought it would be useful to have a more general session on press releases and ask science writers what they want.

The next day I wrote a summary of this session idea and tweeted about it, but it was too late to get input from people. Because of this, I wasn't very confident that the idea would be accepted, and I didn't even bother mentioning it to colleagues. So, I was excited to receive an email from Bora Zivkovic a few weeks ago, inviting me to moderate the session I had suggested. Bora's first suggestion for a co-moderator fell through and to fill this spot I passed along the names of several talented young science writers who - as far as I knew - hadn't regularly attended ScienceOnline meetings: Nadia Drake, Lisa Grossman, Elizabeth Landau, Jason Major, Adam Mann and Rebecca Rosen. I admitted it was a biased list because all of them had written about astronomy.

Bora explained that he'd tried for three years to entice Nadia Drake to come to a ScienceOnline meeting. Nadia has been writing about astronomy and astrophysics for Science News since September 2011. Bora asked her again and this time she said yes. So, our session on improving press releases is going ahead.

I later found out that Bora turned down a number of "old hands" so that about a third of the moderators would be new. I applaud him for this, as it's important to be inclusive and it's clear that there is great interest in attending the meeting. Registration spots quickly filled up in the two windows
available and about 330 people signed up for a lottery to fill the last 75 spots.

I'd also like to commend the organizers of ScienceOnline2013, Bora, Karen Traphagen and Anton Zuiker, who have been doing an excellent job. To give you an idea of what goes into organizing a meeting like this, including finding sponsors so that costs are reasonable, please read this blog post by Anton.

I'm looking forward to the conference and meeting some of the people I've interacted with on Twitter. It's been noted that there are an unusually large number of people attending who are heavily involved with astronomy. Besides Nadia and me there is Alan Boyle, Tania Burchell, Charles Choi, Kelle Cruz, Jeff Foust, Matthew Francis, Pamela Gay, Nicole Gugliucci, Katie Mack, Kelly Oakes, and Catherine Qualtrough. A lot of science online is astronomy-related, so it's appropriate for it to be well represented.

The next steps will involve planning for the meeting. There is a wiki for starting our "session page" to begin discussion before the event. Bora emailed suggestions on how to use and promote this. I have plans for several blog posts about how we do publicity, and about my thoughts on alternatives to the traditional methods. I would be happy for Nadia to add her thoughts in guest blog posts, if she's interested.

As a kind of pre-meeting event, there are plans for a tweet-up at the next AAS meeting in January, where I'll get to meet Nadia and a number of other ScienceOnline2013 and Twitter acquaintances people for the first time. This is another good spin-off from Twitter: encouraging people to be more social.


(*) Just kidding about that one. My nerd cred is robust: just ask my wife.

Thursday, October 4, 2012

More on the Supernova That Wasn't Until It Was

At the end of last week I wrote about a very interesting new paper that appeared on the arXiv: "The Unprecedented Third Outburst of SN 2009ip: A Luminous Blue Variable Becomes a Supernova" by Jon Mauerhan et al. If you didn't read that post, please go ahead and do so now, as I have some new details about the supernova and the super-fast write-up by the authors.

SN 2009ip. Credit: J.Mauerhan et al.

I contacted the first three authors of the paper and asked for comments, and received the following good replies. First, Alex Filippenko from University of California, Berkeley, acknowledged the work of the first two authors by saying:
"Nathan and Jon were amazing in getting all this together quickly,
but we've long had an interest in SN 2009ip and had been monitoring
its latest developments with great interest."
Then Nathan Smith from the University of Arizona added some details about the significance of the result:
"I would just add one thing that Alex alluded to.  There have been several cases (SN1987A and about a dozen others) where astronomers have seen a nearby supernova and then gone back to data archives and identified the star that exploded … after the fact.  This is the first time in the history of astronomy that we were actually studying the star before it exploded and had in fact written papers about it already.  In other words, seeing this thing go supernova could be seen as dumb luck - and admittedly there is luck involved here - but there is also a very good reason why we were interested in this particular star.  For the last 6 or 7 years, I've been going around at conferences and giving colloquium talks about how we think Luminous Blue Variable (LBVs) explode to make Type IIn supernovae (*).  I've gotten a lot of flack for this from theorists with stellar evolution models that don't allow this to be the case."
Now that they appear to have witnessed an LBV destroyed by a supernova, Nathan and the rest of the team have good reason to feel excited by the new observations and vindicated by them.

The light curve of SN 2009ip. The brightness increases as the magnitude decreases, so the 3rd outburst is brighter than the 1st and 2nd outbursts. Credit: J.Mauerhan et al.

Finally, the first author, Jon Mauerhan from the University of Arizona, added some comments about the initial faintness of the supernova and the remarkable speed of the observing team in publishing data that was fresh off the telescope:
"We think the latest brightening of SN 2009ip is the result of the supernova blast wave hitting circumstellar material ejected by the LBV during its prior eruptions. So, it remains to be explained why the supernova remained so faint initially (Mv=-14.5) when we first detected the high velocity spectral features. If circumstellar material were not present to light things up, would SN 2009ip have remained at such a faint level? This is why we brought up the subject of "failed supernovae" in the paper. 
An excellent group effort definitely helped in getting this out fast. We began writing the paper after we noted the high-velocity features in our first bok spectrum on Sept 17th. So the figure-making programs were written, and ready to accept new data as it came in. 
But as you suspected, a tolerance for "lack of sleep" was definitely involved in getting the data reduced and into the paper so quickly, and I appreciate you recognizing that. For example, I reduced the latest bok spectrum at dawn in the observatory dorm kitchen after we closed up, as well as the photometry on the most recent images that were also rapidly reduced and sent to me by Alex's team. After that, I was able to squeeze in a 2 hour nap before waking up to iterate on some new text with Nathan and make the arXiv submission deadline before the weekend. It was a very fun and exciting but rather exhausting couple of days."
In a further comment provided by Jon he explained that the early faintness of SN 2009ip might be explained by shells of material ejected in previous outbursts obscuring the light from the supernova. Much remains to be learned about the event, since it hasn't been monitored for along, as they point out in the paper:
"At the time of writing, this supernova event is just beginning, so we do not know the detailed nature of the supernova event or how bright it will become."
These results for SN 2009ip are one of many exciting results obtained over the last few years in supernova studies, including the discovery of SN 2006gy, another Type IIn event and for a time the most luminous supernova known. In their paper, Nathan Smith and co-authors, including Alex Filippenko, argued that SN 2006gy may have been a "pair instability supernova", where the core of the massive progenitor star produces so much gamma ray radiation that some of the energy from the radiation is converted into particle and anti-particle pairs. The resulting drop in energy causes the star to collapse under its own huge gravity. After this violent collapse, runaway thermonuclear reactions ensue and the star is obliterated, spewing the remains into space. This is a different type of event from most supernovas, which usually occur when massive stars exhaust their fuel and collapse under their own gravity, followed by an explosion.

An illustration explaining the pair instability trigger for a supernova. Credit: NASA/CXC/M.Weiss
A pair instability supernova is a spectacular way for a star to end its life, as they should be the most powerful thermonuclear explosions in the universe, if they exist. One reason they're important is that all of the elements produced inside the massive star are blasted into space, available later to form into stars and planets. If a black hole forms in the collapse, some or all of this material is locked up forever.

The idea of a pair instability supernova for SN 2006gy is testable, because it made specific predictions about how the light curve would behave over several years, based on the radioactive decay of nickel and cobalt.  Further studies showed that the light curve was not dropping at the predicted rate, which means that the pair instability model probably does not apply.

Another supernova, SN 2007bi, has been claimed to be a good candidate for a pair instability supernova, by a team that includes Alex Filippenko as a co-author. However, other models have been suggested by different groups, including a core-collapse model and a model for a strongly magnetic neutron star, so the idea that SN 2007bi was a pair instability supernova is not without controversy.

How is this discussion relevant for SN 2009ip? The authors are not arguing that this supernova was a pair instability event, but they do consider the possibility that the outbursts seen in 2009 and 2010 were driven by the pulsational pair instability. This is triggered by the same pair instability that should lead to a bright supernova, but the explosion isn't powerful enough to tear the star apart and only the outer part is ejected. The mass of the destroyed star is close to that predicted by theory for the range where the pulsational pair instability should cause pre-supernova outbursts.

I am looking forward to hearing about what SN 2009ip does next and to future supernova discoveries.


(*) A Type IIn supernova is caused by the collapse of a massive star. The "II" means that hydrogen was seen in the spectrum and the "n" means that narrow emission lines from hydrogen are present, often indicating that debris from the explosion is interacting strongly with material surrounding the destroyed star.