Tuesday was another busy day at the 224th meeting of the American Astronomical Society (AAS), held in Boston. In addition to a press conference about the Sun’s current weak sunspot cycle, I attended one about galaxy discoveries. This opened with an announcement about a newly observed structure heating gas in the galaxy cluster MACS J0717.5+3745 (MACSJ0717 for short).
Astronomers combined radio and X-ray observations of the MACS J0717.5+3745 cluster of galaxies, and found that the hottest X-ray-emitting gas coincides with a shock front that’s visible in radio radiation. /// photo by X-ray: van Weeren, et al.; Radio: Bill Saxton, NRAO/AUI/NSF; Optical: NASA
A typical cluster of galaxies holds hundreds to thousands of galaxies and a huge amount of multi-million-degree gas (so much gas, in fact, that it outweighs the mass from stars by nearly 10 times). The specific galaxy cluster they looked at is actually a collision site, where four smaller galaxy clusters have merged. During this process, astronomers expect that the gas collides, too, and is heated as a result. This is precisely what Reinout van Weeren of the Harvard-Smithsonian Center for Astrophysics and colleagues saw in MACSJ0717.
They used the Karl G. Jansky Very Large Array in New Mexico to study the object in radio wavelengths and compared that to Chandra X-ray Observatory images of the gas. They also made a temperature map of the gas and compared that to where the radio radiation is the strongest. And sure enough, the hottest temperatures aligned with sharp radio structures. So what is going on? Somehow the shock front is bumping the particles’ energies way higher. During the collision, particles pass back-and-fourth across the collision front, increasing their energies.
Another neat result using X-ray radiation concerned my personal favorite galaxy, M51 (the Whirlpool). Roy Kilgard of Wesleyan University in Middletown, Connecticut, and colleagues used Chandra to stare at the galaxy for hours and then looked at the light. This galaxy is an interesting target because it’s about two-thirds of the Milky Way’s size but has much more star formation (it actually converts about seven times more material to stars than our galaxy does). This rate is a consequence of M51’s two galaxies (the spiral and smaller dwarf) interacting. Kilgard’s team found between 350 and 400 X-ray sources in the galaxy, and the X-ray emission seems to correlate with hydrogen-alpha emission — which makes sense as both X-rays and hydrogen-alpha mark star-forming regions.
New observations of the Whirlpool Galaxy (M51) uncovered some 450 X-ray sources. Astronomers think 10 are binary systems holding stellar-mass black holes. /// photo by X-ray: NASA/CXC/Wesleyan Univ./R. Kilgard, et al.; Optical: NASA/STScI
During the press conference, Kilgard said that his team sees 10 X-ray sources with luminosities that suggest the sources are stellar-mass black hole systems. Each of these objects would be a binary system that had hosted massive stars. One has since evolved and collapsed into a black hole, while the other star is still living and donating material to its companion black hole. As that material nears the black hole, it glows in high-energy radiation, like X-ray, via friction and other interactions.
The Milky Way has a fine example of this — Cygnus X-1. But M51, Kilgard says, hosts 10 of them. Eight of those are associated with regions of star formation, and thus they’re tracing incredibly active massive-star formation in the Whirlpool. They’re seeing a small window of time, when the most massive stars are evolving; these types of stars don’t last too long.
The afternoon and morning press conferences outlined a few more exciting findings in extragalactic astronomy and solar astrophysics:
- Astronomers unveiled a new view of the Hubble Ultra Deep Field with ultraviolet observations added. This allows them to probe “teenager” galaxies — those that were vigorously forming stars around 5 to 10 billion year ago.
- Using the Fermi Gamma-ray Space telescope, scientists looked at about 1,000 blazars — a galaxy with a supermassive black hole at its center that accelerates particles to light-speed. Observer looks down the barrel, essentially.
- Solar astrophysicists described their 30 decades of observations of the Sun’s hot outer atmosphere — called the corona. They found that the corona’s temperature during the recent sunspot maximum was lower than previous maxima. “There’s no doubt that the minimum between the two solar cycles and also the maximum of this solar cycle are behaving different” than previous solar cycles, said Richard Altrock of the Air Force Research Laboratory during a press conference.
I also attended a session about the just-approved K2 project — the make-lemonade-out-of-lemons mission using the Kepler spacecraft. When launched in March 2009, Kepler’s goal was to figure out how rare Earth-size planets are. It made great strides in this science topic until July 2012 and May 2013, when two of its four reaction wheels (which control where the scope is pointed) failed. The satellite needs three wheels to remain fixed at the 150,000-plus stars that it stared at while looking for small dips in light. (Those brightness changes could signify a planet crossing in front of a star, blocking the light.)
NASA recently approved the K2 mission, which uses the Kepler exoplanet-hunter telescope and reorients it so that it points along the solar system’s plane. The born-again mission will observe all types of celestial objects, and be essentially a community instrument. /// photo by NASA
But with only two wheels, Kepler was destined to fade away.
In early fall of 2013, the Kepler team sent out a call to the astronomical community: What can you do with the Kepler craft with just two wheels? One idea was to use the remaining wheels to control the Y-axis and Z-axis and the thrusters to control X-axis (roll) while photons from the Sun would help balance the craft. The spacecraft would be limited to fields of view along the ecliptic (the path that the Sun and its major planets make across the sky), and to observations of about 80 days, due to the Sun’s position — the craft needs our star to provide solar power, but it would have to change position so that sunlight doesn’t saturate the telescope.
In mid-May, NASA officially approved K2. The mission is now community-led, meaning astronomers send in proposals of what fields to point the scope at and what targets to image within that field. The community then peer-reviews those proposals. The Kepler team will process the collected data during those 80-day observing campaigns, which will then be immediately archived and available to everyone. K2 will be an open-source data analysis project, too. And the targets will cover all areas of astronomy: star clusters, galaxies, active black holes, supernovae, exoplanet searches, and others.
I’m excited to hear what discoveries scientists make with the revamped mission. It will be an exciting next few years.
If you want to read more abut Monday’s AAS activities, check out yesterday’s blog post.