At present, the nearest known star is Proxima Centauri which lies at a distance of 4.24 light years from the Sun. Proxima Centauri is a red dwarf star and it is way to faint to be visible with unaided eyes from Earth. Nevertheless, Proxima Centauri is likely to be part of a triple star system with Alpha Centauri - a pair of sun-like stars located slightly further away at 4.37 light years. Although Alpha Centauri is a binary star system, it appears to the unaided eyes as a single star with a combined visual magnitude of -0.27, making it the 3rd brightest star in the night sky after Sirius and Canopus. Alpha Centauri and Proxima Centauri have not always been the nearest stars to the Sun. Over the course of time, a number of stars have been predicted to have come or will come much closer to the Sun.
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Figure 1: Distances of the nearest stars from 20,000 years
ago until 80,000 years in the future. Credit: Matthews, R. A. J. (1994)
Alpha Centauri and Proxima Centauri are predicted to come as
close as 3 light years from the Sun about 27,000 years from now, before
receding away. They will continue to remain as the nearest stars until about
33,000 years from now. Beyond that, a red dwarf star named Ross 248 will become
the closest star to the Sun between 33,000 to 42,000 years from now.
Looking further into the future, a star named Gliese 710 is
particularly interesting since it is travelling nearly head-on towards our Sun.
Even though this star is currently about 64 light years away, it is estimated
to have a high probability of approaching within a mere one light year from the
Sun at approximately 1.4 million years from now. As a result, Gliese 710 is
likely to perturb the Oort cloud and send an influx of comets into the inner
solar system. However, the increase in impact rates in the inner solar system
due to the influx of comets is expected to be very small.
About 7.3 million years ago, a triple star system named
Algol passed within 9.8 light years of the Sun. Although it may not seem like a
very close approach, Algol has a combined mass that is 5.8 times the mass of the
Sun. In addition, the combined luminosity of Algol is a whopping 100 times the
luminosity of the Sun. At closest approach, the gravity from Algol might have
been sufficient to perturb the Oort cloud. An observer on Earth at that time
would have seen Algol shining as a brilliant star with a visual magnitude of
about -2.8. That is over 3 times brighter than Sirius appears at present.
Currently, Algol is about 93 light years away.
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Figure 2: An image of Sirius - the brightest star in the
present night sky. Credit: Greg Parker, New Forest Observatory
Zeta Leporis is another star which came relatively close to
the Sun in the past. Bobylev & Vadim V. (2010) estimated a closest approach
of 4.16 light years from the Sun about 861,000 years ago while García-Sánchez
et al. (2001) estimated a closest approach of 5.34 light years from the Sun
about one million years ago. Zeta Leporis is 14 times more luminous than our
Sun and if it had came as close as 4.16 light years, it would have appeared as
a very bright star in the night sky with a visual magnitude of about -2.5.
On 11 March 2013, the discovery of a binary brown dwarf
system located at a mere 6.5 light years away was published in a paper by Kevin
Luhman, an associate professor of astronomy and astrophysics at Pennsylvania
State University. The last time a stellar /substellar object was found to be
this close to the Sun occurred nearly a hundred years ago in 1916 when Barnard’s
star was discovered at 6.0 light years from the Sun. This binary brown dwarf
system is designated WISE 1049-5319 since it was detected by NASA’s Wide-field
Infrared Survey Explorer (WISE). Such a discovery shows there are still objects
left to be found even within those few light years of space that define the
Sun’s neighbourhood. The discoverer of WISE 1049-5319 said: “There are billions
of infrared points of light across the sky, and the mystery is which one - if
any of them - could be a star that is very close to our solar system.”
References:
- Matthews, R. A. J. (1994), “The Close Approach of Stars in
the Solar Neighbourhood”, Quarterly Journal of the Royal Astronomical Society Volume
35: 1-9
- Bobylev, Vadim V. (2010), “Searching for Stars Closely Encountering
with the Solar System”. Astronomy Letters Volume 36 (3): 220-226
- García-Sánchez, J.; Weissman, P. R.; Preston, R. A.;
Jones, D. L.; Lestrade, J.-F.; Latham, D. W.; Stefanik, R. P.; Paredes, J. M.
(2001), “Stellar Encounters with the Solar System”, Astronomy and Astrophysics
Volume 379 (2): 634-659
- Garcia-Sanchez, J.; Preston, R. A.; Jones, D. L.;
Lestrade, J.-F.; Weissman, P. R.; Latham, D. W. (1997), “A Search for Stars
Passing Close to the Sun”, The First Results of Hipparcos and Tycho, 23rd
meeting of the IAU, Joint Discussion 14
- K. L. Luhman (2013), “Discovery of a Binary Brown Dwarf at
2 Parsecs from the Sun”, arXiv:1303.2401 [astro-ph.GA]