Is Our Galactic Black Hole Blowing Bubbles?

The Cosmic Companion
Sep 12 · 4 min read

Giant bubbles of gas, hundreds of light years long, have been spotted adorning our galaxy. What are they, and why haven’t we seen them before now?

A pair of enormous gas bubbles have been discovered on either side of our home galaxy by astronomers working with a new network of radio telescopes. These structures are among the largest objects ever seen near the center of the Milky Way.

The bubbles, composed of thin deposits of hydrogen gas, stretch hundreds of light years in length. The barbell-like pair may be the result of a massive burst of energy near the core of our galaxy a few million years ago, but the root cause of that event remains a mystery.

The center of our galaxy is accompanied by a pair of large bubbles that could be the product of an ancient cataclysmic event. Image credit: Oxford/SARAO

“We don’t know whether the activity which formed this structure was related to the supermassive black hole at the center of the galaxy, or a number of supernovae all going off at the same time,” explained Dr. Farhad Yusef-Zadeh of Northwestern University, in an exclusive interview with The Cosmic Companion.

Every Galaxy Needs a Supermassive Black Hole

Virtually all major galaxies contain a supermassive black hole (SMBH) near their center. The SMBH near the core of our own galaxy is relatively calm compared to similar objects found in other galaxies.

The region around supermassive black hole at the center of our galaxy, Sagittarius A* (pronounced “Sag A star’ and abbreviated Sgr A*) is seen near the center of this image, taken by the Chandra X-ray Telescope. Image credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI

“Even so, the Milky Way’s central black hole can — from time to time — become uncharacteristically active, flaring up as it periodically devours massive clumps of dust and gas. It’s possible that one such feeding frenzy triggered powerful outbursts that inflated this previously unseen feature,” said Ian Heywood of the University of Oxford.

The bubbles encase more than a hundred magnetic filaments, discovered by Dr. Yusef-Zadeh in the 1980’s. The origin of these filaments — tens of light years in length, but just a light year or so thick — remains a mystery.

The nearly identical size and shape of the bubbles suggests the objects are the end product of a cataclysmic event over a short period of time, which shot mass. in opposing directions, through the interstellar medium.

“This eruption was possibly triggered by vast amounts of interstellar gas falling in on the black hole, or a massive burst of star formation which sent shockwaves careening through the galactic center,” William Cotton, an astronomer with the National Radio Astronomy Observatory, suggests.

“A single poem, alone can turn tides
scatter galaxies and burst forth with rivers from paradise.”
― Sanober Khan, A Thousand Flamingos

These regions are an area of contrasts — making it an ideal target for scientific exploration. Electrons, traveling at speeds near the speed of light travel through wispy clouds of hydrogen and trace gases. This action lights the structure in radio waves, invisible to the naked eye, but an easy target for MeerKAT.

“There is a causal connection between the alignments of the magnetic fields of the filaments and bubbles,” Yusef-Zadeh tells The Cosmic Companion.

The close association of the bubbles and filaments suggests that the event which created the bubbles also resulted in the acceleration of electrons through the filaments, creating the radio signals recorded in this study.

KAT Radio? I’d Listen!

The MeerKAT network of radio telescopes in South Africa. Image credit: SKA South Africa

The MeerKAT radio telescope in South Africa was employed for a study of the core of the galaxy, where radio astronomers often find interesting targets. This investigation unexpectedly revealed the large, unexpected structures hiding in background data.

Radio images were recorded over a wide area around the center of our galaxy. Electrons moving near the speed of light though magnetic fields can produce radio waves, in a process referred to as synchrotron radiation. This signal, with a wavelength around 23 centimeters, easily penetrates the dusty environs found near the center of the Milky Way.

The development of MeerKAT was essential for the discovery of these twin bubbles which, until now, remained hidden in the bright radio signals coming from the center of our galaxy.

An aerial view of a portion of the MeerKAT array. Image credit: SKA South Africa

MeerKAT consists of 64 antennae, each collecting signals which are combined together into a single image. The facility is a testing ground for the future Square Kilometer Array (SKA), a larger network of radio telescopes scheduled to go online in the coming decade.

First envisioned as the Karoo Array Telescope (KAT), the name of the observatory was updated as the South African government increased the scope of the program, expanding the observatory a total of 64 radio telescopes. The current name, MeerKAT, is a variation of “More KAT.” Operated by the South African Radio Astronomy Observatory (SARAO), MeerKAT is the largest science project in Africa.

Structures like the one discovered in this study are commonly seen throughout space, but such galactic evolution had never before been detected in our home galaxy.

“What’s so exciting is seeing familiar activities you find elsewhere, here in our own galaxy,” Yusef-Zadeh exclaims.

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The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

The Cosmic Companion

Written by

James Maynard is the author of two books, and thousands of articles about space and science. E-mail:

The Cosmic Companion

Exploring the wonders of the Cosmos, one mystery at a time

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