I thought Hurricanes had powerful winds. The strongest wind ever recorded was a gust up to 400 Kph near a tropical cyclone in Australia. But Earthbound wind has nothing on Galactic wind. Around the time when our ancestors were just learning to walk upright, the core of the Milky Way Galaxy unleashed a blast of gasses and material at 2 Million Kph.
Millions of years later, we see the aftermath of this eruption as two massive bubbles of material blown out above and below the galactic centre, at least 30,000 Light Years tall!
The lobes were discovered by the Fermi Telescope around 5 years ago as a gamma ray feature in the sky, and have since been called ‘Fermi Bubbles.’ They are clearly visible in the image above. Since their discovery, Astronomers have looked at the bubbles in X-ray and Radio waves to help study their structure and origin. But it’s the Hubble space telescope that was needed to understand the growth rate and composition of the bubbles.
Using the new data, astronomers hope to calculate the mass of material being blown out of the Galaxy, in an attempt to determine the origin and cause of the structures. There are two competing scenarios that could explain the bubbles: A rapid burst of star formation near the galactic centre, or an incredibly massive outburst from our Galaxy’s central Black Hole.
Hubble’s Cosmic Origins Spectrograph (COS) has probed the ultraviolet light from a distant quasar that lies beyond one of the lobes. By looking at the Doppler shift and other properties of the light as it travels through the lobe, we can determine the velocity, composition, and temperature of the expanding gas inside the bubble.
Even though astronomers have seen winds of this magnitude in distant Galaxies, it’s exciting to see some fireworks in our own Galactic backyard. “When you look at the centers of other galaxies, the outflows appear much smaller because the galaxies are farther away,” said Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland, lead researcher of the study. “But the outflowing clouds we’re seeing are only 25,000 light-years away in our galaxy. We have a front-row seat. We can study the details of these structures. We can look at how big the bubbles are and can measure how much of the sky they are covering.”
The Hubble results show that the bubble partly consists of Carbon, Silicon, and Aluminum, indicating that the outburst swept up the heavy elements produced within stars, representing the remnants of ancient star formation. The super-hot gas in the outflow is thought to be up to 18 Million degrees Celcius, but Hubble’s instruments measured a much cooler temperature of 17,000 Degrees, suggesting that the outflow has swept up cooler gas from the disk of the Milky Way.
There are approximately 20 Quasars whose light passes through the bubble on it’s journey to Earth. The results are the first to come in from the study of light of a single Quasar. Once the rest of the sample is completed, Astronomers will have a accurate measure of the properties of the bubbles, giving us insights into how they were formed, as well as a deeper understanding of the extreme conditions in the centre of the Milky Way.