Pluto’s Increased Entourage

NASA and ESA released this great picture from the Hubble Space Telescope this week, showing tiny Pluto’s entourage of moons, imaged twice with a week apart. Three of these were already known – Charon, Nix and Hydra – but Hubble managed to spot a fourth one in there too. It has a diameter of somewhere between 13 and 34 km, roughly 100 times smaller than the best-known moon Charon. The new moon been given the preliminary name P4, which will be replaced by something a little more meaningful in due course. Very neat!

With this, I’m off on holiday for a couple of weeks. No blogging, here or elsewhere.

Image: NASA/ESA/M. Showalter

 

Lemaître: Lost in Translation

Hubble's famous plot, showing the linear relationship between galaxies' distance and radial velocity (from Hubble, 1929)

ResearchBlogging.org The name of Edwin Hubble is ubiquitous in modern astronomy. Telescopes, constants, laws, galaxy classification schemes are named after the famed astronomer, considered to be the godfather of modern astronomy. If he were alive today, he would have appeared on The Simpsons, Southpark and Saturday Night Live. But a number of recent papers posted to the Arxiv and presented at conferences are calling into question Hubble’s claim to fame, and even his integrity as a scientist.

At the root of these questions lies the work of a well-known Belgian astronomer, Georges Lemaître. As a semi-Belgian I felt it my duty to look into the story and blog (and thanks to fellow Belgian astronomer Geert Barentsen for the tip).

Hubble published his seminal result showing a linear relationship between the distance to galaxies (or extra-galactic nebulae, as they were still known then) and their radial (i.e. recession) velocities in a 1929 paper in the Publications of the National Academy of Sciences, carrying the title “A relation between distance and radial velocity among extra-galactic nebulae”. He uses a decade of observations at Mount Wilson Observatory to derive the fundamental relationship empirically. As a result, Hubble is widely credited as the first scientist to show incontrovertibly that the Universe all around us is expanding.

But was he really the first?

In early June, Sydney Van den Bergh, an astronomer based in Victoria, Canada, posted a short note to the Arxiv, recalling a meeting with Georges Lemaître, a Belgian priest and theoretician based at the Catholic University of Louvain. In 1927, two years earlier than Hubble, Lemaître published a paper in which he demonstrates the expansion of the Universe from both observations and theory. Using published distances and velocities, he derives the constant of proportionality between galaxies’ distance and velocity, the number now known as Hubble’s constant H0.

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20 Years of Hubble

Source: Hubblesite.org. Credit: NASA, ESA, and M. Livio and the Hubble 20th Anniversary Team (STScI)

Today we celebrate the 20th anniversary of the launch of the Hubble Space Telescope. Hurrah! Although it’s clearly impossible, as I haven’t aged more than, oh, 10 years since then.

The folks at NASA and ESA have released a set of gorgeous new images and videos of the Carina Nebula, a region of active star formation in our Galaxy.

The European Hubble team have also taken the occasion to launch a rather nice looking new website, check it out here.

The same team are organising a competition to find the most artistic, funniest, weirdest, largest and smallest manifestations of Hubble and its images in popular culture – that’s a fun idea. Anyone can join the Flickr group and submit images, and the category winners get some cool prizes. Read more here.

Google joined in the celebration with a lovely doodle for the day:

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Not a planet, still interesting

Despite Mike Brown‘s best efforts, Pluto is not dead (yet). These cool new images of the tiny non-planet taken with the Hubble Space Telescope show that it is by no means a boring lump of icy rock. When comparing these images, taken in 2002-2003, to a previous set dating back to 1994, scientists noticed some striking changes. This would suggest that Pluto, just like many bodies in the solar system, shows seasonal activity and all kinds of interesting chemistry as it moves along its looong orbit around the Sun.

Image: NASA, ESA, and M. Buie (Southwest Research Institute)

Puffing up elliptical galaxies

ResearchBlogging.org

Elliptical galaxies are the boring uncles of the galaxy family: they’re amorphous blobby things, ubiquitous in the Universe, that contain a fairly uniform population of old, red stars. Without the interstellar gas and dust that is needed to harbour pretty sites of star formation, they are supremely unphotogenic. But they have far more going on beneath their featureless surface: the complex dynamics inside many ellipticals show evidence of a turbulent past and, with many of the most massive known galaxies in our local Universe being ellipticals, they clearly play an important role in galaxies’ evolution.

glazebrook_ellipticals

Studies seem to suggest that high-redshift elliptical galaxies are more compact than their present-day counterparts (figure from Glazebrook, 2009)

Observational surveys of elliptical galaxies at high redshift have in recent years revealed a further interesting fact: ellipticals at high redshift appear to be much smaller in size than those in our local Universe, but have about the same mass and density of stars. In a recent ApJ paper, Ivana Damjanov of the University of Toronto and collaborators describe how a sample of elliptical galaxies at redshifts 1 to 2 looked 2-3 times smaller than those in the local Universe. The first surprise lies in that they evolve at all between redshift 2 and 0. In our current understanding of galaxy formation and evolution, ellipticals are the “red and dead” endpoints of evolution.

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