Some objects we interpret as black holes may not be so – a new study has theorised – but could instead be ultra-compact objects called gravastars, which look like black holes from the outside.
The study conducted by two theoretical physicists at the Goethe University Frankfurt calculated that a new universe filled with dark energy could form inside an imploding massive star, preventing it from collapsing into a black hole.
To cut the clutter, let us look into how black holes are formed and how gravastars differ in their evolution.
Massive stars spend their lives generating enormous amounts of light and heat through a process called nuclear fusion. But eventually, even the largest of them run out. When that happens, the outward pressure that once kept gravity at bay disappears – and the star begins collapsing under its own weight, theoretically compressing all of its mass into a single, infinitely small point known as a singularity.
This singularity is hidden by an event horizon, beyond which nothing, not even light, can escape. This region of spacetime is called a black hole.
Black holes are widely accepted by physicists, yet they continue to raise questions that science cannot fully answer.
For instance, how can a mass equivalent to billions of Suns be squeezed into a point with no size? How can the known laws of physics – which break down entirely at a singularity – be trusted to describe what lies beyond the event horizon?
For decades, a small but persistent group of researchers has explored the possibility that some objects identified as black holes could instead be gravastars – short for gravitational vacuum condensate stars.
Like black holes, gravastars would be extraordinarily dense and massive, making them difficult to distinguish by observation. But crucially, they would contain neither a singularity nor an event horizon.
Instead, beneath their outer layers of ordinary matter, they would be filled with dark energy – a mysterious form of energy that produces an outward pressure, counteracting gravity and preventing the star from collapsing entirely.
For many physicists, this makes gravastars a conceptually appealing alternative. There is, however, one problem that has gone unanswered for roughly 25 years: how could gravastars actually form in the first place?
Theoretical physicists Daniel Jampolski and Professor Luciano Rezzolla of Goethe University proposed what they describe as the first dynamic solution to Albert Einstein’s equations of General Relativity that explains how a collapsing star could produce a gravastar.
According to their work, when a massive star collapses, the process may trigger the birth of a miniature universe within the collapsing matter itself – not entirely unlike the Big Bang that gave rise to our own cosmos.
Just as in our universe, dark energy would drive the expansion of this newly formed interior universe.
As the mini universe expands, it pushes outward against the inward pull of gravity. Under certain conditions, the outward pressure can halt the collapse before a black hole ever forms. The result is a stable equilibrium between the collapsing stellar material on the outside and the expanding interior universe within – and that, the researchers say, is a gravastar.
“The Big Bang of the emerging universe can unfold once the star has already collapsed almost to the point of becoming a black hole,” Jampolski explained.
Jampolski, who developed the solution during his master’s thesis under Rezzolla’s supervision, notes that the conditions required for this to occur are almost incomprehensibly extreme.
At such extraordinary densities, the behaviour of matter remains deeply poorly understood – and that uncertainty, the researchers argue, leaves the door open to entirely new physical phenomena.
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“It is easier to imagine that the Big Bang occurs only at a very late stage, when matter has already been compressed to an extreme degree, thereby giving rise to new effects,” said Jampolski.
Rezzolla said that proposing an alternative to black holes is not the same as dismissing them, and that they still are the natural and simplest solution to the fate of gravitational collapse.
“It is essential to maintain an unbiased approach towards what we do not know and hence explore both the accepted wisdom and the more exotic interpretations. History teaches us that it is not unusual for the latter to become the former,” he said.
In other words, what would sound exotic today could become part of accepted science tomorrow.
(This article is curated by Nityanjali Bulsu, who is an Intern at The Indian Express)
