The supermassive black hole (SMBH) at the center of the Milky Way Galaxy weighs in at four million times as massive as the Sun, yet this giant of spacetime is a sleeping giant. Astronomers have long realized the black hole at the center of our galaxy currently lies dormant, although the reason for this behavior remained a mystery. Recent examination of a massive, spiral-shaped whirlpool of magnetic field lines could provide the answer to this cosmic conundrum.
The Stratospheric Observatory for Infrared Astronomy (SOFIA), managed by NASA, was utilized to examine Sagittarius A*, the SMBH at the center of the Milky Way Galaxy, less than 26,000 light years from Earth. Researchers found this object (abbreviated Sgr A*, but known to its friends as ‘Sag A Star’) may be prevented from consuming matter due to the influence of a powerful spiral-shaped magnetic field.
“The spiral shape of the magnetic field channels the gas into an orbit around the black hole. This could explain why our black hole is quiet while others are active.” explains Darren Dowell of NASA’s Jet Propulsion Laboratory.
Magnetic fields are invisible, so they cannot be directly imaged, and finding detailed evidence of their actions on matter remain elusive. Still, magnetic fields affect the behavior and movement of charged particles and ions, altering the formation and development of planets, stars, and galaxies. By pulling matter away from the black hole, into a stable orbit, these fields prevent Sgr A* from feeding.
“This is one of the first instances where we can really see how magnetic fields and interstellar matter interact with each other,” Joan Schmelz, Universities Space Research Center astrophysicist at NASA Ames Research Center, said.
The View from Up Here is Incredible…
Supermassive black holes (SMBHs) appear in most galaxies. In many of these families of stars, this massive object is active, consuming gas and dust. As matter spirals into these black holes, the process emits a wide variety of radiation, including infrared light (which we on Earth normally experience as heat). If we could see these wavelengths of infrared light with the human eye, we would see them sitting just beyond red within rainbows of light.
Astronomers using the High-resolution Airborne Wideband Camera-Plus, HAWC+, aboard SOFIA, searched the center of the galaxy in far-infrared light. These wavelengths provide the opportunity to study dust grains near Sgr A*, which align with the magnetic fields of our local SMBH, like iron fillings on a piece of paper laid over a magnet.
“At radio wavelengths, the brightest feature of this region is the point-like radio source Sagittarius A* (pronounced “Sag A star”). This source is a compact object, and approximately one Astronomical Unit (1 AU is about 93 million miles) in size, which is much smaller than our solar system (Neptune is 2.8 billion miles from the Sun),” the UCLA Galactic Center Group reports.
Gravity from Sagittarius A* dominates the movement of matter near the center of the Milky Way. Still, understanding the properties of the magnetic field of the Milky Way’s SMBH remained elusive, until SOFIA and HAWC+ set their sights on this massive, mysterious object.
SOFIA is more than just a modified 747SP jet — it is a true flying observatory, equipped with a telescope sporting a diameter of almost 2.7 meters (106 inches). On May 6, 1977, this aircraft was christened into service by Anne Morrow Lindbergh, on the 50th anniversary of the first solo trans-Atlantic crossing by her late husband. The plane was purchased by NASA in 1997, before being subjected to 10 years of upgrades. The re-christening event in 2017 was headed by Erik Lindbergh, grandson to the legendary aviator.
Getting to Know Our Neighbor
“Black holes are the seductive dragons of the universe, outwardly quiescent yet violent at the heart, uncanny, hostile, primeval, emitting a negative radiance that draws all toward them, gobbling up all who come too close…these strange galactic monsters, for whom creation is destruction, death life, chaos order.”
— Robert Coover
The supermassive black hole at the center of the Milky Way was first discovered in 1974, by astronomers Bruce Balick and Robert Brown. In that year, the pair published a paper chronicling their discovery of a bright radio source emanating from a small region of space, near the center of our galaxy.
This object went through a series of names before astronomers settled on Sagittarius A*. One group of researchers suggested the name GCCRS (Galactic Center Compact Radio Source), but that title never caught on, perhaps for the best.
The asterisk in this name is derived from the character used by atomic physicists to denote atoms in an excited state, emitting energy to it’s environment. Brown thought denoting the high-energy region at the center of the galaxy with the same symbol would acknowledge its highly-energetic output.
If Sgr A* is quiet because magnetic fields surrounding it are driving matter into a stable orbit around the black hole, then the behavior of similar quiet SMBHs in other galaxies might be explained as well. Conversely, the feeding frenzy of a highly-active galactic black hole may be the result of magnetic fields aligned in such a way to push material into the dark abyss.
Even for supermassive black holes, having attractive friends, well-aligned with you, appears to pay dividends.