快猫短视频

THE Solar System could be sitting at the centre of a giant optical illusion
that fools astronomers into thinking distant galaxies are accelerating away from
us. The conclusion comes from observations that our galaxy could exist in a
particularly empty region of space.

In 1998, astronomers discovered that distant galaxies appear to be
accelerating away from us. They hypothesised that this acceleration could only
be caused by a mysterious 鈥渄ark energy鈥�. But Kenji Tomita, an astrophysicist at
Kyoto University, says there is an alternative explanation.

Observations hint at a 鈥渨all鈥� of galaxies lying between 650 million and 1
billion light years away from us in all directions, Tomita says. This suggests
that the Milky Way may lie near the centre of a 鈥渓ocal void鈥�, a rarefied region
in which galaxies are scarce and space is expanding unusually quickly.

The difference in the expansion rate, or Hubble constant, would explain why
studies of supernovae in distant galaxies seem to point to a speeding up in the
expansion of the Universe, Tomita says. 鈥淥bservers in a local void feel as if
the Universe at the present stage is accelerating relative to older, more remote
蝉辞耻谤肠别蝉.鈥�

The void scenario can also explain why a supernova 11 billion light years
away appears to have gone off in an era when the expansion of the Universe was
decelerating. This recent observation is considered by some scientists to be
strong evidence of dark energy, demonstrating that its influence did not
overcome the pull of gravity until the Universe had expanded and thinned out.
But Tomita says the void would produce the illusion that closer, younger
supernovae are accelerating and older, more distant ones decelerating.

The idea faces some serious challenges, according to Mario Livio, an
astrophysicist at the Space Telescope Science Institute in Baltimore, Maryland.
For example, observations have shown that the Hubble constant cannot change by
more than a few per cent across distances of up to 500 million light years,
while Tomita assumes that the Hubble constant changes by roughly 20 per cent
across a distance as small as 650 million light years. 鈥淚t will have to be a
very strong argument to convinvce me,鈥� says Livio.