Archive for Scott Tremaine

Scott Tremaine on “Astrohype”

Posted in Astrohype, The Universe and Stuff with tags on February 2, 2014 by telescoper

I recently came across a post by distinguished astrophysicist Scott Tremaine who works at the Institute for Advanced Study in Princeton. The piece is entitled “Overblown Statements in Press Releases Undermine Science”, something that exercised me so much that I invented the category Astrohype so I could post particularly egregious examples on this blog.

Soctt Tremaine’s piece is on the American Astronomical Society website, but I’m reposting the text here to give it wider circulation as I think it makes some very important points that we’d all do well to heed. And of course in the interest of full disclosure I should point out that I am a theoretical astrophysicist myself, so may be a bit biased…

–o–

In a recent column, AAS President David Helfand argued correctly that negative public messages about subfields within our own discipline, or even about other disciplines — “shooting inward at each other” — damage all of us.

Consider, then, the following public messages:

  • from a major research university, a press release titled “Astronomers Discover Planet that Shouldn’t Be There,”
  • from the European Southern Observatory, a press release titled “Turning Planetary Theory Upside Down,”
  • from the National Radio Astronomy Observatory, a press release containing the quote, “Much of what we thought we understood about the physics of pulsars and neutron stars may be wrong,”
  • from the Space Telescope Science Institute, a press release stating, “New observations from NASA’s Hubble Space Telescope challenge 30 years of scientific theory about quasars,” and
  • from a respected news organization, an interview with a prominent exoplanet researcher containing the quote, “Theory has struck out.”

The point is not whether these messages provide accurate characterizations of the state of theoretical understanding in their respective subject areas (though in most cases they do not). The point is that by belittling and trivializing the efforts of theoretical astrophysicists — who try to understand extremely complex processes in exotic environments, with limited clues from observations — they damage the public perception of the entire astronomy community. As just one example, statements from press releases such as those above are often repeated on creationist websites, where they carry extra weight because they have the imprimatur of NASA or a major observatory or university.

Advances in observational astronomy are spectacular enough to appeal to the public on their own merits, without “shooting inward” at efforts to understand these observations. Astronomers and press officers can provide a more realistic picture of the synergy between observation and theory, and in so doing would improve the public perception of astronomy research in particular and of the scientific enterprise more generally.

Dark Matter: Dearth Evaded

Posted in Astrohype, The Universe and Stuff with tags , , , , , , on May 23, 2012 by telescoper

While I’m catching up on developments over the last week or so I thought I’d post an update on a story I blogged about a few weeks ago. This concerns the the topic of dark matter in the Solar Neighbourhood and in particular a paper on the arXiv by Moni Bidin et al. with the following abstract:

We measured the surface mass density of the Galactic disk at the solar position, up to 4 kpc from the plane, by means of the kinematics of ~400 thick disk stars. The results match the expectations for the visible mass only, and no dark matter is detected in the volume under analysis. The current models of dark matter halo are excluded with a significance higher than 5sigma, unless a highly prolate halo is assumed, very atypical in cold dark matter simulations. The resulting lack of dark matter at the solar position challenges the current models.

In my earlier post I remarked that this  study   makes a number of questionable assumptions about the shape of the Milky Way halo – they take it to be smooth and spherical – and the distribution of velocities within it is taken to have a very simple form.

Well, only last week a rebuttal paper by Bovy & Tremaine appeared on the arXiv. Here is its abstract:

An analysis of the kinematics of 412 stars at 1-4 kpc from the Galactic mid-plane by Moni Bidin et al. (2012) has claimed to derive a local density of dark matter that is an order of magnitude below standard expectations. We show that this result is incorrect and that it arises from the invalid assumption that the mean azimuthal velocity of the stellar tracers is independent of Galactocentric radius at all heights; the correct assumption—that is, the one supported by data—is that the circular speed is independent of radius in the mid-plane. We demonstrate that the assumption of constant mean azimuthal velocity is physically implausible by showing that it requires the circular velocity to drop more steeply than allowed by any plausible mass model, with or without dark matter, at large heights above the mid-plane. Using the correct approximation that the circular velocity curve is flat in the mid-plane, we find that the data imply a local dark-matter density of 0.008 +/- 0.002 Msun/pc^3= 0.3 +/- 0.1 Gev/cm^3, fully consistent with standard estimates of this quantity. This is the most robust direct measurement of the local dark-matter density to date.

So it seems reports of the dearth were greatly exaggerated..

Having read the paper I think this is a pretty solid refutation, and if you don’t want to take my word for it I’ll also add that Scott Tremaine is one of the undisputed world experts in the field of Galactic Dynamics. It will be interesting to see how Moni Bidin et al. respond.

This little episode raises the question that, if there was a problem with the assumed velocity distribution in the original paper (as many of us suspected), why wasn’t this spotted by the referee?

Of course to a scientist there’s nothing unusual about scientific results being subjected to independent scrutiny and analysis. That’s how science advances. There is a danger in all this, however, with regard to the public perception of science. The original claim – which will probably turn out to be wrong – was accompanied by a fanfare of publicity. The later analysis arrives at a much less spectacular conclusion,  so will probably attract much less attention. In the long run, though, it probably isn’t important if this is regarded as a disappointingly boring outcome. I hope what really matters for scientific progress is people doing things properly. Even if it  don’t make the headlines, good science will win out in the end. Maybe.