PDF version of this graph
PDF version of this graph
PDF version of this graph
PDF version of this graph
| The
figure on the right shows the Solar System as it is now, with Mercury, Venus,
Earth and Mars orbiting in relatively close orbits around the Sun. The large gas planets Jupiter and Saturn are in wide
orbits. Uranus, Neptune, and
Pluto are even further out, and not visible on the scale of this
diagram. An
asteroid belt extends from a distance of about 450 solar radii from
the Sun out to about
720 solar radii. The Sun produces the energy it radiates away, 400 million
billion billion Watts, by the nuclear fusion of hydrogen deep in its
core. PDF version of this graph |
|
| As the
Sun evolves through its stellar life cycle, it will eventually
burn all the hydrogen content of its core, and start to swell up to
become a red giant. During this phase, it will sweep up the inner
planets Mercury, Venus, and proably the Earth as well. But while growing to a red
giant, the Sun will also lose about half of its mass, and as a
consequence Mars, the asteroids, and the outer planets will move
further out. This will happen in about 5 to 8 billion years from now. PDF version of this graph |
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| Once
the outer envelope of the red giant is dispersed, the core of what
used to be the Sun shrinks into an Earth-sized object, still containing
about half the mass that the Sun once had: a white dwarf has formed.
This compact star is initially very hot, more than a hundred thousand
degrees but, devoid of
nuclear energy, it is condemned to cool down as time passes, with its
planets and asteroids relentlessly orbiting around it. PDF version of this graph |
|
| Eventually,
one of the asteroids may be dislodged form its nearly circular orbit
by the gravitational pull of Jupiter, and be sent on a course
that will bring it very close to the white dwarf. The strong
gravitational field will tidally disrupt the asteroid as it gets too
close to the white dwarf, and the rocky and metal-rich material of the
asteroid will then be evaporated by the radiation from the
hot white dwarf and form a ring of gas rotating closely around the
white dwarf (note the different scale compared to the three figures above). It is this that we have detected around the white dwarf
SDSS1228+1040, which has been cooling for about 100 million years
since the red giant phase: a disk of elements
such as calcium, magnesium, and iron, orbiting the compact star
at a distance of only 1.2 solar radii with a velocity of more than
1000 kilometers per second.
In that respect, our observations of SDSS1228+1040 resemble a glimpse
into the remote future of our own solar system. PDF version of this graph |
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