by Bholes are missing– Objects so dense that nothing can escape their gravitational pull – are among the most striking predictions of General Relativity, a model of gravitational attraction proposed by Albert Einstein over a century ago. They crouch unseen in the midst of galaxies, feeding on stars and interstellar debris.
They’re also a clear indicator that general relativity’s days as the best explanation of gravity are numbered. This theory states that the core of a black hole is a point of infinite density and pressure called a singularity. This, says Chris Pearson RAL Space, Britain’s national space research laboratory, is a mathematical impossibility.
A variety of tastier alternatives have been suggested, but none have the observational evidence needed to support them. Two new works in which Astrophysical Journal And Astrophysical Journal Lettersco-written by dr. Pearson, let’s change that.
The papers’ authors scoured astronomical data for information about black holes at two stages in their lives. The first variety were juveniles in the centers of new galaxies, where stars are forming at high speeds. The second were older examples in galaxies where star formation has stopped. The second group shows what fate has in store for the first according to their suspicions. To their surprise, the researchers found that the ancient black holes had grown ten times faster than cosmological models would predict. But they think they know what could happen.
Previous work has shown that in general relativity, the compression of matter beyond a certain point can result in the formation of a zone containing vacuum energy, the background energy of empty space. Therefore, rather than an infinitely dense singularity, it is possible that black holes contain a source of such energy, the presence of which would explain the observed mass discrepancy. “This,” says Dr. Pearson, “is the first time there has been observational evidence connecting these theories to the real world.”
More radical implications follow. One of the most mysterious features of the universe is that the expansion that began with the Big Bang is accelerating. The driving force is referred to as “dark energy,” but no one knows what it actually is. In a daring theoretical leap, Dr. Pearson and his colleagues suggest that the pockets of vacuum energy present in black holes could be responsible.
What would make this possible is that the properties of vacuum energy depend on the size of the universe as a whole. An expanding universe, theorists say, would contain vacuum energy at ever-increasing densities. This means not only that black holes would increase in mass in ways that have not yet been explained, but that their growth would fill the universe with vast reservoirs of energy. In other words, they could be sources of dark energy.
The team’s calculations show that the size and number of black holes in the universe would be sufficient to explain all of the measured influence of dark energy. The neatness of this statement is remarkable, but elegance is not proof of truth. Much more work is required to ignore other, albeit less spectacular, possibilities. ■
