Milky Way: Just-Right Explosion Rate

Milky Way: Just-Right Explosion Rate

Massive thunderstorms; earth-shattering quakes; climate-altering volcanic eruptions. Such extreme conditions on Earth seem like cap gun shots compared to what regularly happens in the vast reaches of the cosmos.

As one example of the violence occurring in outer space, astronomers found a galaxy that experienced regular explosions a trillion times more powerful than the biggest atomic bomb. These extragalactic blasts highlight a finely tuned aspect of our Milky Way Galaxy (MWG).

Habitable galaxies must form––among other conditions––multiple generations of stars to build up the metals (astronomers’ lingo for elements heavier than helium) that planets require. If star formation proceeds too rapidly, the gas reservoir for future stars depletes before metal rich stars form. (On the other hand, an inefficient star formation rate results, in metals forming too slowly for planets to ever exist.)

Most galaxies (like the MWG and larger) contain a massive black hole (a few million to billion times the mass of the Sun) at their center. During the early stages of galaxy formation, this black hole grows prolifically and its growth affects the star formation rate.

The green and red splotch in this image is the most active star-making galaxy in the very distant universe. Nicknamed “Baby Boom,” the galaxy is churning out an average of up to 4,000 stars per year, more than 100 times the number produced in our Milky Way Galaxy.

Specifically, as the black hole grows, it releases enormous amounts of energy that can blast the gas reservoir out of the galaxy. Astronomers observed evidence of such an outflow in a relatively common galaxy (named SMM J1237+6203) in the early universe.1 The energy required to generate the “outflow” was equivalent to a trillion atomic blasts occurring every second for tens of millions of years!

These observations help explain properties of massive galaxies near the MWG. Star formation ceased billions of years ago in these galaxies because not enough gas remained for additional stars to form. An outflow, like the one observed in SMM J1237+6203, occurring billions of years ago in these nearby galaxies would have removed almost the entire gas reservoir.

How’s the Milky Way Galaxy different? As astronomers model how galaxies form and develop, these outflows play a central role in explaining the observed properties of galaxies. Without the outflows, star formation proceeds too rapidly, yet too strong of an outflow shuts down star formation too quickly. Either way, stars with habitable planets never form. The MWG almost certainly experienced a period with a large outflow. However, this outflow appears to have been fine-tuned to prevent stars from forming too rapidly and without destroying the gas reservoir that ultimately led to the Sun’s existence.

Immensely powerful forces operate throughout the universe, yet those forces interacted so precisely that a benign, life-friendly planet like Earth exists. What or who is responsible for harnessing those interactions? RTB ascribes this work to the careful planning of a benevolent Creator.

  1. D.M. Alexander et al., “Searching for Evidence of Energetic Feedback in Distant Galaxies: a Galaxy Wide Outflow in a z≈2 Ultraluminous Infrared Galaxy,” Monthly Notices of the Royal Astronomical Society 402 (2010): 2211–20.