Slumbering at the Heart of the Milky Way

We live in a galaxy with a black hole at its heart. Such a thing is not unheard of the universe. Many galaxies have at least one black hole at their cores, some have more than one. The Milky Way’s black hole is called Sagittarius A*, or Sag A* (pronounced “SADGE A-star”) for short. Sag A* lies in the constellation Sagittarius, just off the spout of the Teapot shape. The region where the black hole lives is about 26,000 light-years away from us, and is orbited by a swarm of stars. Astronomers have measured the paths of those stars and that information let them determine the mass of Sag A*:  four million times the mass of the Sun. Unfortunately, the visible light from the region is blocked by clouds of gas and dust. However, the black hole itself and its neighboring stars give off many different wavelengths of light, ranging from radio and infrared to ultraviolet, x-ray, and gamma-rays. Detectors sensitive to those wavelengths give us a whole new window on goings-on in the core of the Milky Way, including measurements of stellar orbits and determining the temperatures of gases that appear to stream out from the core.

Sag A* is something of a quiescent black hole right now. That is, it’s not pouring out as much of a torrent of radiation from its accretion disk area and jets as other, more massive and busy black holes do from the hearts of their galaxies. it does glow in various wavelengths of light, but it’s not as active as some of its cousins.

However, our galactic black hole does occasionally swallow up a cloud of gas and dust, and in return belches out hot gases through its jets. On very rare occasions in galactic history, Sag A* undergoes huge eruptions. The last one took place about 2 million years ago, and it shot filaments of gas out to well beyond the galaxy. The trail of gas from this cataclysm is called the Magellanic Stream, and its glow caught the attention of astronomers.  This stream is evidence of a major cataclysm. Infrared and x-ray satellites have detected a powerful outflow of material (sometimes referred to as a “wind”) from the center of the galaxy. There are also “Fermi bubbles”, large globes of gas billowing out from the region around Sag A* and visible in gamma-rays and radio frequency emissions. According to Dr. Philip Maloney of the University of Colorado in Boulder, these point to something big. “All these point to a huge explosion at the center of our galaxy,” he said, referring to what astronomers call a Seyfert Flare.

You may have heard of Seyfert galaxies—they have radio-loud centers, indicating the presence of something very energetic, like a black hole accretion disk and jet. They’re named after Carl Seyfert, the astronomer who first characterized these objects. The idea that our galaxy was once more Seyfert-like is rather interesting, and tells astronomers the Milky Way’s history is more active than expected.

Right now, the stream is emitting light in a manner that is familiar to anyone who has seen northern or southern lights here on Earth.  In the stream, ultraviolet light from nearby stars and active regions splits hydrogen atoms into protons and electrons. When those components recombine, the electrons give off what is called “H-alpha” emission—a specific wavelength of light that is given off by excited hydrogen gas molecules. The brightest glow in the stream comes from the region nearest the galactic center.

Astronomers know that the galaxy’s stars don’t produce enough UV light to account for this glow, and they very likely didn’t in the past. This is because the galactic center never formed stars at high enough rates. There simply aren’t enough stars to do the job.  So, the logical hypothesis is that our galaxy’s black hole swallowed something pretty big in the past, and the resulting “eruption” belched out the glowing stream we see today.

Is it possible Sag A* will do it again?  Absolutely.  Think of it as a dormant volcano sleeping until there’s enough material available to erupt again. There’s a large supply of “star stuff” and gas clouds available to feed the black hole. It’s not a question of “if” but “when”.  In fact, there’s a gas cloud called G2 that will be passing through the galactic center over the next year. Not only could some of it fall into the black hole and set off a new round of explosive interactions, but it could also feed any smaller black holes hiding in the neighborhood. Telescopes sensitive to radio, ultraviolet, x-ray, infrared, and gamma-rays will be able to detect the uptick of activity once G2 hits the scene. So, stay tuned.  Things could get interesting as G2 passes through.

Rain (and Erosion) is One of Them

Back in graduate school I took some geology and planetary science classes where we studied the forces that shape the planets as we see them today—in particular the rocky ones. Every geology student learns that volcanism, tectonism, impact cratering, and weathering are major processes that sculpt planetary surfaces. Volcanism is volcanic action. It expresses itself from volcanoes, like those we see in Hawai’i or Washington, Japan, Indonesia and other hotspots on our planet. Tectonism is most easily thought of as the process that builds mountains, moves plates of material around, and creates fractions in the rocky mantle of our world. Impact cratering occurs when debris from space (meteroids, chunks of asteroids) slam into the surface of a world. Weathering is the process by which water and wind shape the surface. Wind erosion is called aeolian weathering.  Water erosion takes place through the action of running water over a surface.

My area of the world has been subject to the most intense water weathering the past few days and the results are truly disastrous. The Front Range of Colorado (so named because it lies along the front range of the Rocky Mountains) has received upwards of 14 or so inches of rain in only about 2-3 day’s time. To put that into perspective, this is just under our YEARLY expected total of ALL moisture (including snow).  To get it in the space of a few days is truly amazing. And, when you get that much water all at once, devastation occurs.

Experts estimated that the Boulder, Colorado area received about 4 BILLION gallons of water in a very short time. That includes the mountain areas.  Where does all that water go?  In the mountain, it goes downhill. As it does, it picks up speed, plus debris. And by debris, I mean trees, telephone poles, cars, branches, houses, and big boulders—whatever happens to get in the way of the wall of water-borne debris. The destructive power of water moving down the  mountains has torn up roads, homes, towns, and highways. It has upended people’s lives. And it has taken some of those lives.

As I type this, estimates of the missing and unaccounted for people in the towns of Boulder, Estes Park, Lyons, Jamestown, Salina, Big Thompson Canyon, Longmont, and many other communities is up to around 1,200. These may include people who just haven’t had a chance to call and tell someone they’re safe, but at least four people HAVE died in this disaster. There will likely be more. [UPDATE: As of September 23, the number of unaccounted for is in the single digits, and at least 9 people have died as a result of the flooding.  The number of lost homes and destroyed roads is still being tallied.]

The scenes of devastation, like the one above, are just unbelievable. They include houses hanging over crevasses, cars buried in mud and upended like toys. Scenes of flooded fields greet people on the plains east of Boulder, Greeley, Fort Collins and Longmont. In Denver, there are images of cars left abandoned in flooded intersections, flooded yards and neighborhoods, and debris everywhere. (You can see more images at on the Denver Post’s Web site).

Living on an active planet is not always easy. People who live with volcanoes know this very well. If you live in a seismically active area, such as along the San Andreas Fault in California, you know what it’s like to live with the knowledge the next big quake is coming. People who more regularly live with monsoon rainstorms know what it’s like to endure flooding. And now, people in Colorado know what it’s like to have the same very unseasonal monsoons hit our region. These floods are being called 100-year and 500-year floods, so named for the statistical frequency with which they can happen. Clearly they dont’ happen every year. The last big floods I recall were in the 1960s, but even those were not as destructive as the past few days have shown us. And, prior to these latest rains, our area had been getting higher than normal rain fall–unusual for a region that normally gets 15-20 inches a year. So, why did this happen?

There is already knowledgeable talk of climate change playing a role in bringing these rains to our region. As our climate changes, weather extremes become more… extreme. Weather that was once rare in a region is now becoming more commonplace (such as the Arctic warming destroying the sea ice). Warm rains this late in Colorado are not the norm. Scientists are now seeking to understand why we got them. There is an excellent discussion of this very topic, called Inside the Colorado Deluge, published on the blog of the National Center for Atmospheric Research in Boulder, and worthy of reading.

One thing I do know is that these rains and floods are not part of divine retribution or magical spells or anything that smacks of the occult or weird or because there’s gay marriage or women’s lib or atheists or or whatever it is that short-sighted and ignorant people like to blame these things on.

These floods happened because we got a lot of rain, and rainwater does what it does under the force of gravity on a rocky planet with an atmosphere and weather. There are scientific explanations for what has happened.  And, there are psychological reasons why us humans and our animals are devastated by what has happened and we seek to understand and cope with such disasters. Knowing the science behind these happenings helps me, at least, to cope with them. I hope it does for others, although I know that such knowledge will in NO way bring back a lost loved one, a lifestyle, a home, a pet, or a livelihood.

We live on an active planet, in every sense of the word. Lava, earthquakes, rain, snow, and unseasonal weather are part of the gig here. We humans get too comfortable sometimes and forget that our friendly, life-giving planet also presents us with challenges and tests. And how we survive those challenges and tests are part of the lesson we learn as we live here.

Please keep those who have lost their lives, homes, and livelihoods in this disaster in your thoughts. And, if you can send along help, the Red Cross and regional blood banks will be happy to talk to you. The Denver Post has a story about how people can help; check it out.