Pathfinder will let us 'see' big black holes

Detecting and studying gravitational waves would open a new window on the universe. Photo / AP

It has been a century since Einstein presented his theory of general relativity but it is still helping us unveil some of the deepest mysteries of the universe.

Now the LISA Pathfinder mission will prepare the way for us to study violent events that we've never seen before - such as the creation of massive black holes.

The probe is to test technology needed to launch another mission, eLISA, in 2034, which will aim to detect ripples in space known as gravitational waves.

Chasing waves

Gravity is the force that orchestrates the universe, but until now we have only been able to observe some of its most superficial effects. However, the ability to directly detect and study gravitational waves would open a new window on the universe.

Gravitational wave observations would allow us to see intimate details of the creation of massive black holes; supermassive black holes spiralling together and merging as galaxies collide; and neutron stars and black holes orbiting in various pairings until they inevitably spiral inwards and merge.

Seeing directly to the heart of such events will never be possible using normal telescopes that measure electromagnetic radiation.

This is because the excited matter typically surrounding such events would obscure our electromagnetic view which is why a gravitational wave detector could "see" them for the first time.

Big challenge

We need to go into space to catch the richest and most numerous gravitational wave signals. eLISA will be the first space-borne gravitational wave observatory.

eLISA will comprise three satellites in a triangular arrangement with arms of some millions of kilometres. Precision arm length measurements will be made between "test masses" in each spacecraft - freely floating mirrors that reflect the measuring laser beams that will travel along the long arms.

eLISA is a complex mission. But the scientific return would be enormous.

However, the first step is to make certain that the required sensitivity is achievable. To demonstrate this, the LISA Pathfinder mission will fly the test masses and the length measurement system of an arm of eLISA, compressed into a single compact spacecraft.

I led the UK team that has laboured long and hard to develop the laser metrology system for Pathfinder. To us, the launch will be the defining moment.

• Harry Ward is Reader in Physics and Astronomy, University of Glasgow.