Posts tagged space
Posts tagged space
NASA’s SDO Observes Fast-Growing Sunspot
The bottom two black spots on the sun, known as sunspots, appeared quickly over the course of Feb. 19-20, 2013. These two sunspots are part of the same system and are over six Earths across. This image combines images from two instruments on NASA’s Solar Dynamics Observatory (SDO): the Helioseismic and Magnetic Imager (HMI), which takes pictures in visible light that show sunspots and the Advanced Imaging Assembly (AIA), which took an image in the 304 Angstrom wavelength showing the lower atmosphere of the sun, which is colorized in red. Credit: NASA/SDO/AIA/HMI/Goddard Space Flight Center
Structure and Evolution of Galaxies
As much as we know about galaxies, the evolution of galaxies is one of the mysteries of the Universe. By looking far out into space and equivalently, far back into time, astronomers can look at the oldest galaxies and make comparisons with modern-day galaxies to get a sense of how they’re evolving. To really understand galaxy evolution, though, one must understand the details of the structure of galaxies; therein lies many wondrous secrets of galaxies. We will focus on spiral galaxies:
The Structure of Spiral Galaxies
Most spiral galaxies have similar features, the most significant of which include a dark matter halo, the galactic disc, spiral arms, a central bulge (most containing a bar-like structure), and a stellar halo.
The dark matter halo is believed to be the main structural component of the Milky Way galaxy whose functional purpose is primarily to hold together the galaxy; without it, the galaxy would not be gravitationally bound. The dark matter halo is situated well beyond the visible galactic disc which is detected using observations like rotation curves of galaxies. Current observations suggest that dark matter accounts for roughly 95% of the Milky Way’s mass, while the other 5% is accounted for with normal, baryonic matter. It is currently believed that dark matter played a significant role in the evolution of galaxies, initiating clumps of matter in the early Universe which eventually lead to structures like galaxies.
The galactic disc is the location of most of the interstellar medium (ISM, composed of gas and dust) and also contains a substantial amount of stars which orbit in roughly circular orbits confined to the galactic plane; it consists of most of the visible matter in the galaxy. The Sun is located about 8.5kpc (kiloparsecs) from the galactic center in the galactic disc. The spiral arms within the galactic disc are the main sites of star formation; the blue spiral arms are indicators of young, hot stars. Within the galactic disc is where most cosmic recycling occurs and as a result, the ISM has a higher metallicity than primordial gas. The metallicity-age relation is important for understanding galaxy evolution. Most open clusters are found in the galactic disc, but some globular clusters (roughly one third) are found here, as well. Open clusters are very young because they are loosely bound and are easily disrupted. Open clusters have high metallicities because they are formed from more recently formed ISM which has had time to become enriched with metals. In contrast, globular clusters are very old as they are strongly gravitationally bound. Since globular clusters consist of the oldest stars in the galaxy, the metallicity-age relation suggests that they should have very low metallicities but those found in the galactic disc have unusually high metallicities; this suggests that cosmic recycling enriches the contents of the globular clusters.
The stellar halo extends further than the galactic disc itself and is roughly spherical in shape. Here lie roughly two thirds of the galaxy’s globular clusters. The globular clusters found here, as expected, have very low metallicities because they are young and do not get contaminated by the cosmic recycling that takes place in the galactic disc. The stellar halo’s star formation has long since ceased; there is very little ISM left in the stellar halo. The stars within the stellar halo have largely elliptical and highly irregular orbital motions which are not confined to the galactic plane.
What Does Any of This Tell Us About Galaxy Evolution?
Without the dark matter halo, our galaxy wouldn’t be gravitationally bound the way it is today. With this, along with the fact that dark matter consists of 95% of the galaxy’s mass, it is suggested that dark matter played a key role in the initial formation of galaxies. The spiral arms of the galaxy suggest that the galaxy is rotating, which is well supported by observations. Older stars contained in the stellar halo having irregular, elliptical orbits and younger stars confined in the galactic disc having regular, circularized orbits suggests that the galaxy started out in a disordered state which over time settled down to a more orderly state; the galaxy originated as a large gas cloud that eventually collapsed and through the conservation of angular momentum, became a flat, rotating disc. The fact that globular clusters within the galactic disc have unusually high metallicities suggest that cosmic recycling is the origin; as time progresses, high mass stars explode and contaminate the surrounding ISM to further enrich future stars’ chemical composition. Furthermore, globular clusters which were once believed to originate from the Milky Way are now believed to having been captured by the Sagittarius Dwarf galaxy, which suggests that even though the galactic halo is the oldest component of the galaxy, it is still a dynamic part of the Milky Way. Currently, the Milky Way is in a collision course with its neighbour, the Andromeda galaxy. In about 4 billion years, the two spiral galaxies will collide to form what astronomers like to call the Milkomeda galaxy.
A couple of days ago I uploaded the Io, Ganymede transit of Jupiter. Unfortunately, my original video was missing a few frames of the transit, but a fellow astronomer was kind enough to send me the missing images, so here is the finished video of the complete Io, Ganymede transit.
I just need this on my blog.
The footage in this video is derived from image sequences from NASA’s Cassini and Voyager missions.
~1:30, Hank discusses that your body wouldn’t freeze because there’s no medium for your body to transfer heat…. But couldn’t (and wouldn’t) your body lose heat via thermal radiation? Clearly, radiation doesn’t require a medium. Regardless of whether it would freeze, I don’t see how your body wouldn’t lose heat via thermal radiation. Anyone?
(Not including Earth)
Our of curiosity, I made a survey for this. Mostly because I’m interested in what people consider “interesting” when it comes to these things, but also whether or not that impacts how much you like it. But please do not answer the questions unless you have an actual answer for both of them. In other words, don’t just choose one randomly without giving it any thought.
The survey can be found here. I’ll post the results a week from today, on January 13th.
The full album “Cosmogenesis” by the instrumental djent/progressive metal (one man) band Gru. I need to add some variety to my playlist in terms of genre anyway.
I am so happy to see other people listening to this band. This is an incredible album.
Why Explore Space?
In 1970, a Zambia-based nun named Sister Mary Jucunda wrote to Dr. Ernst Stuhlinger, then-associate director of science at NASA’s Marshall Space Flight Center, in response to his ongoing research into a piloted mission to Mars. Specifically, she asked how he could suggest spending billions of dollars on such a project at a time when so many children were starving on Earth.
Stuhlinger soon sent the following letter of explanation to Sister Jucunda, along with a copy of “Earthrise,” the iconic photograph of Earth taken in 1968 by astronaut William Anders, from the Moon (also embedded in the transcript). His thoughtful reply was later published by NASA, and titled, “Why Explore Space?”
This is worth a read.
NASA’s Curiosity rover and its parachute were spotted by NASA’s Mars Reconnaissance Orbiter as Curiosity descended to the surface on Aug. 5 PDT (Aug. 6 EDT). The High-Resolution Imaging Science Experiment (HiRISE) camera captured this image of Curiosity while the orbiter was listening to transmissions from the rover. Curiosity and its parachute are in the center of the white box; the inset image is a cutout of the rover stretched to avoid saturation. The rover is descending toward the etched plains just north of the sand dunes that fringe “Mt. Sharp.” From the perspective of the orbiter, the parachute and Curiosity are flying at an angle relative to the surface, so the landing site does not appear directly below the rover.
The parachute appears fully inflated and performing perfectly. Details in the parachute, such as the band gap at the edges and the central hole, are clearly seen. The cords connecting the parachute to the back shell cannot be seen, although they were seen in the image of NASA’s Phoenix lander descending, perhaps due to the difference in lighting angles. The bright spot on the back shell containing Curiosity might be a specular reflection off of a shiny area. Curiosity was released from the back shell sometime after this image was acquired.
This view is one product from an observation made by HiRISE targeted to the expected location of Curiosity about one minute prior to landing. It was captured in HiRISE CCD RED1, near the eastern edge of the swath width (there is a RED0 at the very edge). This means that the rover was a bit further east or downrange than predicted.
The image scale is 13.2 inches (33.6 centimeters) per pixel .
HiRISE is one of six instruments on NASA’s Mars Reconnaissance Orbiter. The University of Arizona, Tucson, operates the orbiter’s HiRISE camera, which was built by Ball Aerospace & Technologies Corp., Boulder, Colo. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter Project for NASA’s Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, built the spacecraft.
Credit: NASA/JPL-Caltech/Univ. of Arizona