Measuring Dark Energy Like a BOSS

When you start to think about the most massive and extreme ‘stuff’ in the universe, you inevitably go to Dark Matter and Dark Energy.  They exist as opposites, one with incredible gravity holding the universe together, and the other a mysterious vacuum energy tearing it apart.  Studying this cosmic tug of war gives astronomers a chance to determine the past and future of the entire universe. To study the immense scale of these two quantities, the Baryon Oscillation Spectroscopic Survey (BOSS) program of the Sloan Digital Sky Survey-III (SDSS) constructed a 3D map of the sky, amounting to a volume...

A Direct Black Hole

How did supermassive black holes form in the early epochs of the universe? More importantly, how did they have enough time to grow as large as they did? The answer requires a very different universe.  And back then, conditions were much different than they are now.  There was a lot of gas, little dust, no stars, and a plethora of dark matter. Astronomers have spent decades observing early quasars, massive active galaxies powered by huge black holes feeding on surrounding gas.  But these galaxies are seen so early in the universe’s history, one starts to wonder how a black hole finds sufficient...

Black Holes ARE Dark Matter?

Dark matter could be almost anything.  With little data other than how much total dark matter mass exists, we can’t decode much about what individual chunks of dark matter might be made of.  I’ve talked before about Massive Compact Halo Objects (MACHOs) and Weakly Interacting Massive Particles (WIMPs), but these are just two possibilities.  Other theorists have talked about Modified Newtonian Gravity (MNG), where gravity may work differently on the grand scale than it does on our small Earth scales.  Or perhaps it’s something I haven’t seen before.  Maybe what we call dark matter is just a large population of ancient black holes....

Dark Matter is Complicated

The fact that we have found gravitational waves tells us that we have come a long way in terms of science and technology.  We detected a perturbation in the fabric of space-time that was one one-thousandth the diameter of a proton.  It’s insane to think about that level of precision.  And yet we still can’t find Dark Matter, the stuff that is literally everywhere in the universe.  Is it our problem? Or is dark matter just on a whole different level? By now, we know that dark matter isn’t some clump of stuff sitting out there in space.  But that...

A Ring of Fire

A direct consequence of Einstein’s theory of general relativity, and an observational way to prove it, is gravitational lensing.  It requires a powerful gravitational source to work, such as a galaxy or cluster of galaxies.  It works in a similar way to a lens of glass, where rays of light are bent toward a single source, increasing the brightness.  In this case, instead of glass, the bending of the rays is due to the curvature of space. Light rays coming from the source would otherwise miss Earth, but instead are bent toward us when there is a massive object in front of it.  It’s...

Building the Supermassive

Black holes form when a massive star runs out of fuel.  Gravity causes the core to collapse down to an object so dense that light itself can not escape.  In the Milky Way galaxy, there are expected to be over 100 Million black holes, though of course we can’t see them.  The one we can see is the supermassive black hole Sag A*, lying deep within the core of the galaxy.  But how did Sag A* form? Was it from the merger of many smaller black holes?  Or is there some other process forming the most enigmatic objects in the...

The Problem With Baryons

Baryonic matter, which is everything we are made of and everything we can see in the universe, is not a lot of stuff.   I mean to a tiny Earthling, it’s a heck of a lot, but if you put it all together it only makes up about 5% of the total Mass-Energy in the Universe.  If you’ve ever seen the Millennium simulation, it highlights the fact that both baryonic and dark matter are organized into filaments of mass, with the baryonic matter at the densest points, ie the galaxies. What lies between these dense nodes and filaments are vast empty...

Gamma Rays Point to Pulsars, Not Dark Matter

Gamma rays are the most powerful form of electromagnetic radiation in the universe.  With wavelengths as small at atoms, they usually result from the most powerful interactions known, such as the collision of two particles, or the release of energy from the accretion disk of a black hole.  But there is another potential source of gamma rays that has not yet been confirmed: Dark Matter. The leading candidate for dark matter is the theorized Weakly Interacting Massive Particle (WIMP), though it is not as wimpy as its namesake suggests, making up 5 times as much mass as the visible matter...

Dark Matter in a Galaxy Cluster

We know that galaxies like our Milky Way are far more massive than we can see.  The dark matter in the Milky Way makes up 90% of it’s total mass.  Another way of saying this is the Mass to Light ratio, comparing the total mass inferred by the rotation speed of the galaxy to the total mass of stars in the galaxy.  This ratio, M/L, for the Milky Way, is about 10.  But for a galaxy cluster, the M/L ratio is more like 100.  Galaxy clusters are not just dense collections of stars and massive galaxies, they are also immense...

A Young Giant Galaxy Cluster

In the early universe, there was a huge amount of swirling matter and light that didn’t really have much structure.  Compared to today’s much more regular dotting of galaxy clusters and superclusters, the early universe was all over the place.  But as will all things, there had to be a first.  a first star, a first galaxy, and even a first galaxy cluster. The massive cluster of galaxies known as IDCS J1426.5+3508 is the most distant massive galaxy cluster ever discovered, and it has some interesting properties that point to how it formed and evolved so quickly.  One such property is...