A supermassive black hole is an almost unimaginable thing — an object with a mass from a million to a billion times our sun’s, yet compressed into a point. The point does not have even the volume of an atom. This singularity is surrounded by an event horizon, which is a region inside which nothing can be seen and from which nothing can escape. Every large galaxy checked for them has at least one gigantic black hole in the center.
Smaller black holes can form when a supernova destroys a star bigger than our sun. The remnant material implodes so quickly that nothing can stop it, and it becomes a black hole. Millions of relatively small black holes might exist in a galaxy.
But astronomers are becoming convinced that huge black holes may have existed since early in the universe’s existence, with galaxies forming around them.
The May issue of Astronomy Magazine points out that nobody knows why it’s true, but scientists have discovered that in our neck of the universe the mass of a galaxy’s central supermassive black hole is 0.14 percent of the mass of the entire galaxy, if it’s an elliptical galaxy. The same ratio, 0.14 percent, holds true for the mass of the black hole compared with the central bulge of a spiral galaxy. The magazine cites an astronomer named Dominik Riechers of the California Institute of Technology, Pasadena, for the calculations.
In many galaxies, including our Milky Way, the black hole is quiet, hardly ever devouring stars. At least for now, few stars wander close enough for it to snag. But in other galaxies, holes are consuming an enormous amount of material.
[A view of M106 (also called NGC 4258) that I took a few nights ago in Emery County. Cumulative exposures amounted to a little more than half an hour]
Matter drawn into a black hole doesn’t just fly directly into it; it first orbits the black hole at high velocity. This material is in a giant accretion disk whirling around the black hole’s periphery, a monstrous cauldron of charged particles. So much energy is generated just outside the hole that it blasts out enormous jets of gas and radiation.
A 2001 article in The Encyclopedia of Astronomy and Astrophysics, produced by Nature Publishing Group and available on-line, says evidence for black holes in active galactic nuclei is mostly indirect, showing up in large variations in brightness, relativistic jets with a stable axis, and high-energy spectra.
Discussing the detection of black holes at the centers of galaxies, the article’s author, Mark Whittle, writes that the galaxy Messier 106 “provides the best case to date for a supermassive black hole….” In the nine years since, many more supermassive black holes have been discovered. But recent studies of M106, located only 22 million light years away, show astounding features of its black hole.
M106 is a barred spiral in the constellation Canes Venatici. The constellation floats high in the heavens on these spring nights, affording the best telescopic views of its wonders.
M106, also known as NGC 4258, “features spectacular, bisymmetric nuclear jets that span nearly the full visual extent of the galaxy,” write G. Cecil, A.S. Wilson and C. De Pree in an article published by The Astronomical Journal on Feb. 10, 1995. The jets once were detectable only in emission lines that appear in spectroscope analysis and in the form of radio waves.
However, Cecil, Wilson and De Pree write that the ROSAT satellite was used to study soft X-ray emissions in the galaxy. The gigantic streams of X-rays result from the jets acting as particle accelerators. “The helically twisted, nuclear jets, previously detected in radio continuum and visual emission-line studies, are found to dominate the X-ray images,” they add.
The summary says, “In the spectacular outflow of NGC 4258 we have found the tightest correlation observed to date between thermal X-rays and a radio jet … [T]hese results suggest that we are seeing hot, shocked gas from nearby molecular clouds … that have become entrained into the jets.”
In 2007, NASA’s Astronomy Picture of the Day feature, located HERE, published a bizarre view of M106. Besides the disk with its spiral arms that are visible in ordinary light, the image superimposes the X-ray and radio wave emissions detected by other means. Suddenly, M106 has a whole new set of spiral arms that don’t line up with those that can be seen visually. In the artificial coloring used, the newly-discovered arms look like blue fins propelling the galaxy through space.
The caption says an analysis of the X-ray and radio data suggests the two extra spiral arms “are composed of material heated by shock waves. Detected at radio wavelength, powerful jets originating in the galaxy’s core likely drive the shocks into the disk of NGC 4258.”
I photographed M106 a few days ago from my favorite astronomy spot in the San Rafael Swell, Emery County. While the telescope was gathering photons that had traveled for 22 million years, I took a short hike.
After the narrow moon had set, light pollution glowing from Price and Castle Dale lit only about five degrees up from a section of the horizon. Switching off my flashlight’s red light, I could see where I was going by starlight.
It was a cold, clear, peaceful night, with the Milky Way arching from southeast to north. A few clouds hugged the horizon. Brilliant points of stars pierced the blackness. However far I went, I could hear my generator chugging away. I walked on the dirt road, reveling in the night sky’s beauty. I picked out constellations and kept track of my whereabouts by noting a camping sign on a pole at the turnoff, dark shapes of pinyon pines, spots clear of brush.
It was a strange conjunction, this quiet and calm night when I photographed M106, a galaxy whose jets of highly charged particles erupt from the accretion disk around a supermassive black hole and scorch out twisting paths of radiation that stretch for tens of thousands of light years.