Dark matter does not slow down when it collides with itself.  These are the latest observations using the Hubble Space Telescope and the Chandra X-ray Space Observatory.

Dark matter cannot be seen.  It does not reflect, absorb or emit light.  But we know it is there because of how its gravity affects other objects.  Scientists use a method called gravitational lensing to measure how much space is warped when dark matter interacts with objects.  The light from distant objects is magnified and distorted due to the gravity of dark matter.

The best place to view this is in galaxy clusters.  Here, galaxies are colliding and interacting with each other.  Seventy two large cluster collisions were studied.  The collisions occurred at different times and were seen at different angles.  By putting all the data together, scientists are able to paint a better picture of how dark matter behaves.

Scientists found that the dark matter continued straight through the collisions without slowing down much.  If the dark matter had any impact on other dark matter, the distribution of the galaxies would have shifted.

This new data can now eliminate some of the theories of what dark matter can be.  Now particle physicists can narrow the number of unknowns when developing their theories.  We are getting closer to an answer, but still have a long way to go before we understand this invisible matter that makes up most of the universe.

NASA's Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft has observed an aurora in the Martian atmosphere and an unexplained high-altitude dust cloud.

The aurora appeared for five days just before Christmas.  MAVEN detected a huge surge in electrons from the sun just before the aurora began.  As these energetic electrons interact with the atmosphere they cause the gas to glow.  This is how we get the northern and southern lights on Earth.

The aurora on Mars traveled very deep into the atmosphere.  Unlike on Earth, Mars lost its protective magnetic field billions of years ago, so the solar particles can strike the Martian atmosphere directly.

The high-altitude dust cloud is a mystery.  It occurred from about 93 miles (150 km) to 190 miles (300 km) above the surface.  What the dust is made of and where it came from is unknown.  The dust may have come up from the surface, or be coming from the moons Phobos and Deimos, or coming from the solar wind, or could be debris from comets.  But no known Martian process can account for it.

ESO's Very Large Telescope (VLT) in Chile has confirmed a dusty gas cloud known as G2 has made it past a black hole intact.  The black hole is the supermassive black hole found at the center of the Milky Way.

Scientists have been tracking G2 for years as it moved closer and closer to the black hole.  It was expected that the forces of the black hole would stretch and tear the cloud apart.  As this happened, activity in the black hole would be detected.  Many telescopes around the world awaited the event.  But as G2 made its closest approach in May 2014, nothing happened.  G2 had been traveling away from Earth at 10 million kilometers per hour and after it swung around the black hole it is now heading toward Earth at 12 million kilometers per hour, gaining speed from the gravitational slingshot effect.

But why did G2 survive?  Why did it not get obliterated?  One answer may be that G2 is not just a cloud of gas.  Inside G2 may lay a young star.  This young star would have enough gravity and mass of its own to avoid being torn apart at that distance from the black hole.

The latest observations have not detected any increased activity in the black hole and G2 is still intact and not significantly stretched or deformed.