Kat-7 Astronomers: Closing on Black Hole mystery

Astronomers could soon be a step closer to unravelling the mystery of why galaxies are smaller than astronomers predict.

From January next year, the Karoo Array Telescope-7 (Kat-7) in South Africa will be able to investigate whether black holes are holding back galaxy growth, as well as probing other phenomena such as gravitational waves and cosmic rays.

Kat-7 has been built in the Northern Cape as a test bed for a 3,000km-wide array that will become fully operational in 2024.

Small black holes, five or 10 times the mass of our Sun, and those up to a billion times larger - deemed "supermassive" - had been thought to only consume matter.

But scientists have discovered that they emit jets of matter too, and - given that massive black holes are believed to lie at the heart of galaxies - these jets could explain why galaxies are smaller than predicted.
The period during which these galactic geysers are active varies with the mass of the black hole.

Those small black holes can be active for a brief period every 20 years. However, supermassive black holes can be active for millions of years and then be dormant for a billion.

These jets can stretch out for up to 100,000 light-years. This means to travel from the black hole to the end of the jet would take 100,000 years travelling at light speed.

The jets are visible to scientists at radio wavelengths. By analysing the jets' radio waves, scientists can gauge how much energy has been released. That amount of energy could be key to understanding the alleged holding back of galaxy growth.