Beyond
snapping extraordinary pictures of faraway nebulas, the revolutionary Hubble
Space Telescope has completely transformed our view of the universe since it
was launched in 1990. By capturing the clearest, deepest images of the cosmos
ever, Hubble has shed light on some long-standing mysteries perplexing
scientists—while uncovering far deeper ones that have yet to be solved.
The push of dark energy
The
universe was born in the Big Bang, but before Hubble, its age was uncertain. By
measuring where distant galaxies are more accurately than ever before and how
fast they are moving as the universe expands, the orbiting telescope resolved
the cosmos is roughly 13.7 billion years old.
However,
at the same time, Hubble and various ground telescopes unexpectedly discovered
that the universe's expansion is accelerating, instead of slowing down
as one might expect due to the pull of gravity from galaxies. The repulsive
force driving this accelerating expansion, dubbed dark
energy, which makes up some 70 percent of the universe, remains "one
of the greatest mysteries in science," said Hubble senior project scientist
David Leckrone.
Dark
energy has prompted new theories regarding the origin of the universe, such as
one where clashing
membranes of reality trigger endless cycles of cosmic death and rebirth, as
well as the fate of the universe, raising the possibility that dark energy ends
the universe in a Big Rip.
Future progress on understanding dark energy's nature will likely require a
dedicated dark energy space mission, "for sometime in the middle of the
next decade, perhaps," Leckrone said.
The pull of dark matter
Galaxies
don't have enough normal matter to hold together the giant clusters of galaxies
they are in, leading scientists to speculate on the existence of gravity from
unseen "dark
matter" pulling to keep galaxies together.
Although
what dark matter actually is remains a mystery, Hubble did help show how
much there is of it out there, by looking for how much dark matter's gravity
warps space-time and thus distorts light from distant galaxies. The space
telescope helped reveal there is some five or six times more dark matter than
normal matter in the universe.
Hubble
also has, with other telescopes, developed the first
3-D map of dark matter. "This helped show the clumpiness of dark
matter has apparently increased over time, showing it exhibits ordinary
gravity, as opposed to something else," Leckrone said. Better
understanding how dark matter behaves could help scientists better understand
what it actually is, he added. In the meantime, the 3-D dark matter map helps
explain "how the
universe acquired the large-scale 'web-like' structure that we observe in the
pattern in which galaxies are distributed over the sky," he added.
Other mysteries solved and unsolved
The biggest explosions in the universe
Satellites
first discovered gamma
ray bursts, the biggest explosions in the universe, in the late 1960s, but
scientists had little idea where they came from. Hubble helped discover they
originated for the most part come from hot, young, very massive stars in
distant galaxies, "which we think catastrophically collapsed on themselves
to produce these gamma ray bursts," Leckrone said. "We believe they
must be going off all over the place out across the universe."
Photographing worlds
Neither
Hubble nor any other telescope so far has directly imaged an exoplanet.
"There was one object that was claimed to be a planet, and it may well be,
but it's a huge distance from its central star and is abnormally bright, so I
don't think it really is," Leckrone said.
Protoplanetary disks
Hubble
was the first to directly image the disks of gas and dust where planets are
born with great detail, pictures sharp enough to reveal the gaps in the disks
that nascent worlds carved out as they orbited their stars. "These
findings help shed light on how worlds form, although there's quite a ways to
go with that research," Leckrone said.
Hubble's successors
The
James
Webb Space Telescope is intended as a significant improvement over Hubble,
an orbital infrared observatory capable of picturing substantially fainter
objects. It might even "have a fighting chance to directly image a planet
around another star," Leckrone said.
As
light shed in earlier ages of the universe naturally shifts toward the
infrared, distorted as it is by the expansion of the universe, Leckrone added
the James Webb Space Telescope should also help peer back to an era unseen
until now, when the first galaxies formed back when the universe was only a few
hundred million years old. Investigating these early galaxies could shed light
on the poorly understood process of how galaxies like our own Milky Way formed.
Still, Hubble will continue to
prove invaluable for imaging the universe at visible and ultraviolet
wavelengths, Leckrone added.
"Although
the James Webb Space Telescope can be viewed as a successor to Hubble, it is not a
replacement for Hubble," Leckrone said. "Ultimately, a much larger ultraviolet-visible
telescope in space will be needed to carry on Hubble's work."
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