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All posts for the month May, 2014

Eileen Meyer — “Measuring the Speeds of Jets from Super-massive Black Holes”

Posted by admin on May 30, 2014
Posted in: DTM Astronomy Seminar.
M87_jet

Hubble Space Telescope image of a 5000-light-year-long (1.5-kiloparsec-long) jet being ejected from the active nucleus of the active galaxy M87. From http://en.wikipedia.org/wiki/Active_galactic_nucleus.

Great talk today from Dr. Eileen Meyer of Space Telescope Science Institute (STScI) about gaseous jets launched from active galactic nuclei AGN.

These cosmic monsters emit a lot of matter and energy, sometimes in the form of jets (see picture at left) that can outshine the rest of the host galaxy. The jets can be observed to span vast distances, thousands of light years, larger than the host galaxies themselves, and mounting evidence suggests that the jets are powered by supermassive blackholes, living deep within the galaxy.

Meyer studies the evolution of these jets, and by following the motions of individual clouds of gas, she can tease out their velocity vectors, critical for understanding the amount of energy and momentum carried by the jets. In some cases, she’s found that the jets can brighten or fade over just a few years, some of the few astronomical objects that can be observed to change appreciably on human timescales.

Understanding the detailed properties of these jets is critical because they are so powerful they can shape the growth of galaxies and even in the evolution of the Universe itself over the largest spatial and temporal scales.

John Debes — “How Dust Around Dead Stars Reveals Galactic Terrestrial Planet Formation”

Posted by admin on May 22, 2014
Posted in: Uncategorized.
This illustration is an artist's impression of the thin, rocky debris disc discovered around the two Hyades white dwarfs. Rocky asteroids are thought to have been perturbed by planets within the system and diverted inwards towards the star, where they broke up, circled into a debris ring, and were then dragged onto the star itself. From http://en.wikipedia.org/wiki/File:Artist%E2%80%99s_impression_of_debris_around_a_white_dwarf_star.jpg.

This illustration is an artist’s impression of the thin, rocky debris disc discovered around the two Hyades white dwarfs. From http://en.wikipedia.org/wiki/File:Artist%E2%80%99s_impression_of_debris_around_a_white_dwarf_star.jpg.

Fun talk today from Dr. John Debes from the Space Telescope Science Institute (STScI) about white dwarfs eating planetesimals.

White dwarfs are the ghostly embers of former stars — they originate when a star (that is small enough not to become a black hole instead) dies and leaves behind a dense core of carbon and oxygen, enshrouded in a thin hydrogen atmosphere. That white dwarf core then slowly cools and darkens over billions of years, basically doing nothing else.

However, many white dwarfs show telltale signs in their atmospheric spectra of rocky materials. Debes, along with others, has suggested that material arises from asteroids that are perturbed by distant planets around the white dwarf. Those orbits take the asteroids so close to the white dwarf host that they are ripped apart by the star’s gravity, producing a cloud of dust and gas that then accretes onto the star.

Astronomers can very accurately measure the composition of that dust, which can actually tell us something about the compositions of asteroids in distant planetary systems. So astronomers can learn about what makes up the planets in distant systems by studying the remains in these planetary graveyards.

Gerónimo Villanueva — “Is Mars Active?”

Posted by admin on May 2, 2014
Posted in: DTM Astronomy Seminar.
Possible processes and chemical reactions in the martian atmosphere. From Villanueva et al. (2013 -- http://www.sciencedirect.com/science/article/pii/S0019103512004599).

Possible processes and chemical reactions in the martian atmosphere. From Villanueva et al. (2013 — http://www.sciencedirect.com/science/article/pii/S0019103512004599).

Great talk today from Dr. Gerónimo Villanueva from NASA Goddard Space Flight Center on organics on Mars.

Villanueva was on the team that reported discovery of methane in the atmosphere of Mars. This discovery is important because methane is thought not to stick around too long on Mars (< 300 years), and so something has to actively produce it for methane to be there now, such as microbial life.

Detecting methane on Mars is difficult from telescopes on the ground on Earth because the Earth’s atmosphere also has a lot of methane in it. In order to see the Martian methane, Villanueva has to do a lot of observing and modeling to rescue the tiny spectral signal of Martian methane from underneaththe whopping terrestrial signal.

According to Villanueva, current observations suggest that, if methane is released into the Martian atmosphere, it is released rarely and not seasonally. In his most recent work, Villanueva did not detect any methane, possibly indicating that methane has an even shorter lifetime in the Martian atmosphere than previously thought. And so work continues to understand this puzzling but tantalizing discovery.