Today’s American Astronomical Society news feed brought me a small handful of press releases. Three releases (1, 2, 3) related to the approximate mapping of the exoplanet HD 189733b, and to the discovery that exoplanet HD149026b is the hottest known world. Cool. The forth and final press release I received was also planetary science related but it’s embargoed, so I can’t really tell you anything beyond that my news feed lead me to believe that astronomers are currently only studying planetary science. The truth is, astronomers are exploring all the heavens have to offer in voracious detail, but the press officers (and press in general) are neglecting a lot of cool science going on in other areas.
Flipping over to the arXiv e-print service, a different picture emerges. The couple dozen submitted works for Wednesday, May 9, spanned subjects from string theory to CMB Anisotropies and the outer Solar System (1, 2). Some papers are still in peer review, and others will never be submitted to journals. All the papers are sitting there waiting to be read and learned from, and hopefully someday cited by someone not on the author list.
A quick survey of the pdfs finds information on the following topics (warning: my choice of grouping may not match yours): satellite orbits, observatory sky brightnesses, high redshift galaxies (2), computer models (3), the sun (2), the CMB, black holes (3), gamma ray bursts (3), star formation, dark matter, star clusters, theoretical astronomy (3), masers, compact objects that aren’t black holes (3), rare star types, galaxy formation, dark energy, supernovae, and galaxy evolution. The authors range from students (including someone I was at the University of Texas with), to senior faculty, to one potential crazy. The field of astronomy is alive and well, and it’s exploring many things that almost no one will ever know about.
I don’t know the exact statistics on how many people are likely to read the typical astronomy journal article within the first year after its publication. I expect that stating a good paper has its abstract read by a few hundred people is probably fair. I suspect that same paper might be read in its entirety by maybe a few tens of people. There are two simple reasons these articles get so little coverage: 1) There are dozens of papers published a day and no one has the time to read all of them and accomplish anything else, 2) Many of these papers are so highly technical that someone not actively doing research in the specific sub-field of the paper won’t be able to understand the content without reading many of the papers referenced as well. So… Except when someone does something that just sounds really cool, or when someone does something picked up by the media, most of what is getting discovered gets ignored.
The media (and the press officers who feed us content) tend to latch on to specific types of content. Anything that can have an adjective like largest, smallest, nearest, farthest, youngest, oldest, is fair game. For whatever reason, Guinness hit on a great thing with their book of world records – People are inherently interested in extremes. Stories related to extremes can sell a magazine/newspaper/TV show, so… That is what gets written about. Almost anything related to a planet (in our solar system or another solar system) can also be made media sellable, as can almost any discovery related to the beginning and end of the universe. These stories touch on the questions we ask as 5-years olds and still hope to have answered as adults: Can we explore other worlds, is there life beyond our Earth, where did we come from, and where are we going? To try and sate their curiosity, people will pay for planet-related publications and ignore the cost of cosmology-centric content. So, the press feed gives the public what they will purchase – in this case planets and cosmic prognostications – and the rest of the cosmos gets ignored.
That’s not to say everything on arXiv is worth publicizing. There is a lot of mind-numbing adding of decimal places to results and theoretical work that just may not result in anything. There is also really good science that is just filling in of details. This is hard and worthwhile research, but not necessarily the stuff Joe Public really needs taking up space in his head. Still, in the midst of all that is going on, there are cool things getting missed.
For instance, there were three neat results potentially worth knowing about in today’s news. In order of upload, the first paper that caught my eye looked at the nearby Leo A Dwarf Galaxy. This little system is a member of our local group, and lurks about 800,000 parsecs (2,600,000 light years) away from the Milky Way. It shows evidence of multiple epochs of star formation and still has hydrogen gas waiting to make some future generation of stars. By carefully measuring the velocities of a dozen carefully chosen stars, a team of Smithsonian Astrophysical Observatory observers lead by Warren Brown determined that Leo A also has significant levels of dark matter. Specifically, Leo A appears to be made of at least 80% dark matter. This result comes from carefully adding up the stars’ luminous mass and then theoretically determining how much additional mass is needed to make the observed stars and previously observed gas orbit Leo A with their measured velocities. This isn’t the first system found with this level of dark matter, but that’s what makes this result so neat for me. High levels of dark matter are typically found in dwarf spheroidal (dSph) galaxies – the little guys that dance in the halos of giant galaxies like the Milky Way and Andromeda. dSph galaxies are generally dead, with no current star formation, and in some cases only one identified past generation of star formation. Leo A isn’t a dSph. It’s a dwarf irregular. I know, subtle difference only an astronomer can love and all that… BUT, Brown and his team point out that as Leo A ages and fades, it will look progressively more like a dSph. We are seeing in this little system what a lively dSph may look like, and demonstrating dark matter is always there in the same proportion. A new evolutionary link is built stronger as this paper works to flesh out how galaxies move through the Hubble classification system.
In a separate result, Kalirai et al. used Keck Observatory to discover unusual white dwarf stars in the old open cluster NGC 6791. This star cluster was formed roughly 8 billion years ago and is one of the oldest known star clusters. It also has an unusually high metal content (which means the gas that formed the stars had been enriched with a lot of material from supernovae and mass loss. In this case, the stars have roughly twice the amount of heavy elements the Sun has.). For complex reasons, many of the red giants in this cluster had high mass loss rates. Normally, red giant stars burn hydrogen in shells around their helium cores (these cores were formed while the stars were on the main sequence and were burning hydrogen to helium like the Sun.) Generally, this hydrogen dumps enough helium onto the core and burns hot enough that eventually the helium core ignites and burns helium into carbon. In stars like our Sun, the carbon core will eventually become the seed of a future white dwarf with a mass greater than 0.46 solar masses. In NGC 6791, however, high mass loss rates prevented the helium from ever igniting, and the stars died as helium-core white dwarfs with masses well under 0.46 solar masses. This is neat to me for a couple of reasons. First, this is a cool path for stellar evolution that doesn’t generally crop up in Astronomy 101. I like being able to point out flaws in text books. Second, this means that in really metal rich systems whole classes of stars, like Mira variables, may not form in large numbers because their progenitors just won’t live long enough. This means that as our universe becomes more and more enriched with heavy metals, the Mira variables so often observed by amateur astronomers may become more rare. It’s a bit of a downer, but still cool.
Just to have full disclosure, the final paper that caught my eye is co-authored by one of my friends from graduate school, David Fisher (primary author is Niv Drory). I have to admit I looked at the paper first because of the topic, and then had a “Cool – I know him” moment when I looked at the author list. The science that caught my eye is a potential new way to use galaxies’ colors to get at additional information. Spiral galaxies can be loosely grouped into those that are blue (actively forming stars and coming in all sorts of “shades” (not a scientific term, exactly) of blue, and red systems that are all very similar in color (falling on the red sequence, scientifically speaking)). Measuring galaxy colors is, in the grand scheme of things one can do with a telescope, fairly easy. The trick comes in understanding what these colors mean beyond the bland “Star forming” and “Not star forming (a lot)” labels. Using the Hubble Space Telescope, Drory and Fisher discovered that spiral systems that are red have classic bulges indicating some sort of a violent event in the past that created this elliptical structure in the middle of the disk and cut off some star formation. In blue systems, however, there is what is called a pseudo-bulge – a stirred up part of the disk – that is blue and indicates the system has thus far escaped harms way. Now, this isn’t a universal rule. A red spiral system that has some dust and gas can be made blue through violent collisions that trigger new star formation, but this color changing event also changes the systems morphology. With these results, it is possible to say that when you find a red, undisturbed spiral, you are finding the survivor of a past collision.
In selecting these stories, my own personal biases come out. I am personally drawn to stories of evolution. We live in a dynamic and changing universe, and we are learning more each day about how each type of object will grow and change throughout its lifetime. The universe, like a forest, is a changing thing whose structure is dictated by the life cycles of its parts. Just as biologists can better understand the rain forest by understanding the life cycles of certain parasites, astronomers can better understand the cosmos by tracing the sometimes odd and unusual life cycles of the stars and the galaxies they live within.