Supermassive black holes in a ‘death spiral’ could collide – what impact will it have on Earth?

Astronomers have identified what appears to be two supermassive black holes that could collide within a century, sending out huge gravitational waves that will be felt on Earth.

The bizarre event, which sees the two black holes engaged in a ‘death spiral’ that will eventually result in a spectacular merging, is located in the galaxy Markarian 501 around 500 million light-years from Earth.

It had previously been classified as a blazar — a bright galactic core typically powered by a single black hole.

However, a new analysis of decades of radio telescope data suggests a more complex picture.

Researchers found evidence of not one but two powerful jets of particles emerging from the galaxy’s core.

Each jet is believed to be driven by a separate black hole, with masses estimated at between 100 million and one billion times that of the Sun.

The findings, published in the journal Monthly Notices of the Royal Astronomical Society, indicate that the two black holes orbit each other roughly every 121 days.

They are separated by a distance of just 250 to 540 times that between the Earth and the Sun — extremely close given their immense size.

Further support for the binary black hole theory came from observations in June 2022, when the alignment of the system caused light from one jet to be bent by the gravity of the foreground black hole, forming what is known as an Einstein ring.

This effect strengthened the case that two supermassive black holes are present.

Scientists say that when the pair eventually merge, the event will generate powerful gravitational waves detectable from Earth— far stronger than those previously detected from smaller black hole collisions.

Such a merger would offer a rare opportunity to study extreme physics on a cosmic scale, although any direct effects would remain far beyond Earth, so we are safe for now.