February 3, 2017

New technique could reveal the sneakiest black holes in the galaxy

While studying the molecular gas around a distant supernova remnant, researchers at Japan’s Keio University have discovered a new way to detected “quiet” black holes – those that don’t generate an accretion disk or which are not strong enough to emit visible radiation.

According to Gizmodo and UPI reports, Keio graduate student Masaya Yamada and professor Tomoharu Oka were using the ASTE Telescope in Chile and the 45-m Radio Telescope at the Nobeyama Radio Observatory in Japan to study gasses surrounding a supernova remnant W44, which is located approximately 10,000 years from our solar system.

Specifically, they sought to measure the amount of energy being transferred from the explosion to the surrounding gas clouds, but as they conducted their analysis, they discovered odd motion within the cloud. They nicknamed this phenomenon the “Bullet,” as it was moving in excess of 223,000 miles per hour and moving in a direction opposite that of the Milky Way.

“Most of the Bullet has an expanding motion with a speed of 50 km/s, but the tip of the Bullet has a speed of 120 km/s,” Yamada noted in a statement.“Its kinetic energy is a few tens of times larger than that injected by the W44 supernova. It seems impossible to generate such an energetic cloud under ordinary environments.”

Two possible scenarios could explain this energetic cloud

Upon their discovery, Yamada and Oka further studied the “Bullet” and came up with a pair of scenarios which could explain what may have caused this unusual phenomenon. Their findings have been published online and in a recent print edition of Astrophysical Journal Letters.

In the first scenario, Gizmodo explained, dense gas close to a black hole could have caused an explosion to occur, causing molecular gas to speed in our direction. In this case, the mass of the black hole would be at least 3.5 times the solar mass, the study authors noted in a statement.

In the second scenario, known as the “irruption model,” a high-speed black hole traveled through a dense gas, dragging that gas with it to form a fast-moving stream. In this situation, the mass of the black hole would be a minimum of 36 times the solar pass. At this point, the researchers state that they are unable to determine which scenario is the more plausible of the two.

No matter the cause, Oka said that the researchers have “found a new way of discovering stray black holes” – a breakthrough, considering that observations have thus far only identified about 60 of the at least 100 million black holes believed to exist in the universe.

The research team plans to continue to use a radio interferometer to collected higher resolution observations of the Bullet, hoping to determine the actual cause of this phenomenon. Shunya Takekawa, Yuhei Iwata, Shiho Tsujimoto, Sekito Tokuyama, Maiko Furusawa, Keisuke Tanabe and Mariko Nomura, all from Keio University, were also involved in the study.


Image credit: Keio University