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FOR a brief, horrifying period this year, the Hubble Space Telescope wasn’t working, and it wasn’t clear whether it would ever get going again. Something was wrong with the electronics and even switching to the backup system didn’t work correctly. This was a deeply emotional time for me and many other members of the astronomy community.

In my case, the death of this orbiting instrument is one of my worst scientific nightmares. When I saw the film Gravity recently, I wept at the scene that depicts Hubble being obliterated by high-speed space debris. I will always classify it as a horror film, not because of what Sandra Bullock’s character endures as she tries to survive the terror of a catastrophic accident in space (which, yes, is pretty rough), but because Hubble’s demise would seem like the end of the world as I know it.

Hubble’s pristine images of deep space have become so culturally ubiquitous that people recognise them without knowing where they come from. An example is Jeff Hester and Paul Scowen’s 1995 images of the “Pillars of Creation” in the Eagle Nebula, a star-forming region. The pictures aren’t just beautiful, they also enhanced our understanding of how stars form.

However, Hubble’s success wasn’t always guaranteed. Nancy Roman, NASA’s first chief of astronomy, is often recognised as the “Mother of Hubble,” advocating for it when there were threats to cancel the overrunning and expensive mission. It took decades and cost billions, but the telescope ultimately launched in 1990, when I was just 7 years old.

Before it had the chance to revolutionise the way we see our universe, Hubble was the subject of high drama in space. It was launched manually by astronauts who piloted it into low Earth orbit on a space shuttle, part of a fleet of craft that is now retired, meaning future instruments are likely to be automatically deployed.

The space shuttle ended up being essential to Hubble’s success though, not just because of the launch, but because initially the instrument suffered from a mirror defect that significantly decreased the quality of its images. In 1993, astronauts flew the space shuttle Endeavour to Hubble and in a series of spacewalks over days, repaired the telescope. It was updated in a similar fashion three more times. The last was in 2009, just before the space shuttle was taken out of operation.

“I classify Gravity as a horror film because the end of Hubble would seem like the end of the world as I know it”

Today, if there is a problem with Hubble, it has to be resolved from the ground, and this is ultimately what happened over the summer, successfully this time. There will be no more physical repairs. I regularly feel anxious about this, as I have spent the majority of my life seeing the universe through Hubble’s optical, infrared and ultraviolet eyes, and my career as a particle cosmologist has been completely shaped by its results.

Today, the Nancy Grace Roman Space Telescope (NGRST) is in the works and will hopefully join Hubble in the sky before this decade is over. NGRST will pursue the cosmic acceleration mystery that was uncovered in the late 1990s using Hubble data.

Along with dark matter, cosmic acceleration is perhaps the greatest open question in cosmology: not only is space-time expanding, but that expansion is also occurring at a rate that is increasing with time, and we don’t know why. I wrote my PhD dissertation on possible explanations for this, and the new telescope promises to .

As regular readers know, I have gone on to become very focused on dark matter, the other great cosmological problem of our time, and Hubble has had plenty to say about this too.

One observational phenomenon that Hubble has been particularly effective at capturing is something called gravitational lensing, where the presence of dark matter distorts space-time so much that light arriving from a galaxy or star takes a noticeably curved trajectory. Sometimes the lensing is so strong that it causes multiple images of one object to appear on a telescope’s detectors. It is a bit like dark matter causing space-time to behave like a funhouse mirror.

Using knowledge of Einstein’s general relativity in combination with observations of lensed objects allows us to characterise basic properties of the clumps of dark matter that caused the distortions in the first place.

Just last year, a team led by , Los Angeles, used this kind of observation to place bounds on the dark matter parameters that characterise the evolution of galaxies and the dark matter halo that we believe surrounds each galaxy.

Hubble has affirmed for us that there is still so much about the universe that we don’t know, even as it continues to help us increase our understanding of it.