Sunday, 22 July 2012

Astrophysics stuff from the week 16-22/7/12

'Study finds heat is source of 'Pioneer anomaly''
This has been a quandary for physicists, for many years, now -- what is causing the mysterious acceleration of the pioneer spacecraft?
It turns out to be caused by the gentle, but persistent push of UV-radiation from the hot side of the crafts.
“The effect is something like when you’re driving a car and the photons from your headlights are pushing you backward,” said Slava Turyshev, the paper’s lead author at NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “It is very subtle.”
"by 1998, as the spacecraft kept traveling on their journey and were over 8 billion miles (13 billion kilometers) away from the sun, a group of scientists led by John Anderson of JPL realized there was an actual deceleration of about 300 inches per day squared (0.9 nanometers per second squared)."
"They saw that what was happening to Pioneer wasn’t happening to other spacecraft, mostly because of the way the spacecraft were built. For example, the Voyager spacecraft are less sensitive to the effect seen on Pioneer because its thrusters align it along three axes, whereas the Pioneer spacecraft rely on spinning to stay stable."
“The story is finding its conclusion because it turns out that standard physics prevail,” Turyshev said. “While of course it would’ve been exciting to discover a new kind of physics, we did solve a mystery.”

[video] 'Simulation: A Disk Galaxy Forms'

[picture] 'Hubble sees the needle galaxy, edge-on and up close'

[video] 'A magnetic monster’s dual personality'
We all know what Pulsars are --  fast-rotating neutron stars, that emit radio waves -- the regular signal-emitters that were misidentified as aliens, all those decades ago.
But magnetars are neutron stars that exhibit the strongest magnetic fields in the universe, and emit masses of x-ray radiation.
Low-field magnetars are variants of these, that have a much stronger internal magnetic field than external, causing internal distortions that lead to pulses of X-ray emission.
Only two examples of these kinds of stars are currently known.

'Astronomers discover exoplanet neighbor smaller than Earth'
While looking at a Neptune-sized planet, orbiting the star GJ 436, astronomers at the University of Central Florida have noticed the presence of another, smaller object, two-thirs the size of Earth, and orbiting so close that its year lasts 1.5 days, and its surface temperature is ~800 Kelvin

'Earliest spiral galaxy ever seen: a shocking discovery'
Spiral galaxies tend to be a lot younger than their elliptic or irregular counterparts, because their orderliness takes time to develop; but this one has been observed as just a few billion years younger than the universe itself!
The astronomers think that the presence of a dwarf galaxy, nearby, might be responsible for its early formation into a spiral.

'NASA sees Sun send out mid-level solar flare'
As the sun reaches solar maximum, in its 11-year solar cycle, we should expect an increased frequency of solar flares coming our way.

'Solar corona revealed in super-high-definition'
"the highest-resolution images ever taken of the Sun's corona, or million-degree outer atmosphere, in an extreme-ultraviolet wavelength of light. The 16-megapixel images were captured by NASA's High Resolution Coronal Imager, or Hi-C, which was launched on a sounding rocket on July 11th. The Hi-C telescope provides five times more detail than the next-best observations by NASA's Solar Dynamics Observatory."

Sticking with the Sun's corona:
'Unexpectedly slow motions below the Sun's surface'
The HMI (Helioseismic and Magnetic Imager) on board NASA's SDO (Solar Dynamics Observatory) has observed an impressively slow speeed of convection in the corona - just a few metres per second.
This evidence necessitates a rethink of theory, underlying solar material dynamics (which wasn't very concrete in the first place).
The data, however, does rely on inference from surface observations, to determine currents thousands of kilometres down, inside the Sun. I wonder how large a source of error this might be.

'XENON100 sets record limits for dark matter'
Don't forget to get excited about negative results, LOL
Teams at the LHC and the Tevatron produced negative results for years, before finding the Higgs Boson - the negative results simply told them what the Higgs wasn't.
It might turn out that dark matter (as opposed to light matter, which interacts with electromagnetic radiation) isn't in the form of WIMPs at all, but we won't find out without experiment.
Roll on, the negative results!

No comments:

Post a Comment