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In this Creation magazine reprint of a 1994 article titled Exploding stars point to a young universe, Young-Earth Creationist, Jonathan Sarfati argues that the scarcity of Supernova remnants (SNRs) in the sky suggests the Milky Way galaxy is less than billions of years old.

On average, a galaxy like our own, the Milky Way, should produce one supernova every 25 years.

[...]

As can be readily seen above, a young universe model fits the data of the low number of observed SNRs. If the universe was really billions of years old, there are 7000 missing SNRs in our galaxy.

Does astronomy predict a Milky Way supernova every 25 years? Are there missing SNRs that undermine these predictions?

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  • Removed comments suggesting heavier-than-Iron elements are proof of Supernova Remnants. Answers don't belong in comments, and it is a strawman. See the definition of SNR.
    – Oddthinking ♦
    Dec 5, 2016 at 14:13
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    Is 7000 missing even significant? That's not even one million years.
    – user11643
    Dec 5, 2016 at 15:25
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    @fredsbend: It was tricky to find a self-contained excerpt that included the claim from this article. Read the article to see that they are claiming 7000 missing of about ~7300 expected.
    – Oddthinking ♦
    Dec 5, 2016 at 23:35
  • Even if this was true, it would make the age of the Milky Way millions of years old instead of billions. It would not make it thousands.
    – vsz
    Dec 6, 2016 at 7:55

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There are many reasons why this is wrong. The first one is the assumption of 1 supernova per 25 years. That was the value arrived at in Gustav Tammann's article published in 1970. Others got values up to 100 years (Tammann himself changed his value later). All these values are really only good guesses.

Worse errors are made in the percentage of remnants that should be visible. To start with, only a small percentage of them are visible; the others are obscured by dust in the galaxy. This does not happen to the same extent to the supernovas themselves, as they are intrinsically very much brighter.

Sarfati also uses an old paper to come up with the number of remnants in the Large Magellanic Cloud (a satellite galaxy to the Milky Way). However, that figure was considered to be wrong (and much smaller) in later studies. Older remnants are very difficult to distinguish against a background of dust in the galaxy. Many of them disappear completely after about 10,000 years or so.

It should be noted that, using Sarfati's own reasoning, we should not be able to see any remnants older than 6000 years. Instead, we know of remnants (e.g. G166.2 + 2.5) that are over 100,000 years old. How did those originate in his universe? The same goes for the distance to supernovas. The distance to SN 1987A has been trigonometrically measured at 167,000 light years (the paper says 51,200 parsecs). In other words, its light took more than 30 times longer to reach us than the creationist universe has supposedly existed.

Remember also that a supernova typically becomes either a pulsar or a black hole, both of which are very hard to observe. A black hole can only be "seen" through its effects on other matter, and a pulsar is mainly visible if the solar system happens to be in line with its sweeping radio beam (with some pulsars the star itself has also been seen). Hence, all we can see of them long after the event is an expanding cloud of gas that gets dimmer over the millennia.

There are several other reasons which are covered in a very good article on TalkOrigins. That article has links to all the original scientific papers referred to, so you can check the validity yourself.

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    You should add the sources you are using.
    – Mindwin Remember Monica
    Dec 5, 2016 at 14:02
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    Please cite (1) the non-1-in-25 numbers, (2) that Tammann renounced his earlier estimate, (3) that old SNRs are not visible, including the 10,000 year figure (4) that G166.2 + 2.5 is over 100,000 years old. You should also show the kpc->light year conversion you've used. (5) supernova become pulsars/black holes, and they are hard to observe.
    – Oddthinking ♦
    Dec 5, 2016 at 14:19
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    "All these values are really only good guesses." Arguably values form before roughly 1995 aren't even good guesses. Computational astrophysics underwent a huge change in the 1990 making all the old jokes about astrophysicists putting the error bars in the exponent obsolete in about a decade. Then the "era of precision cosmology" comes along in the mid naughties.
    – dmckee --- ex-moderator kitten
    Dec 5, 2016 at 16:54
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    Note that you don't generally observationally determine the supernova rate by counting supernovae. As pointed out, obervational effects prevent one from seeing the remnants very well in the disk of the galaxy. Even the supernovae themselves may be obscured HEAVILY by dust. For example, the probable progenitor of Cassiopeia A should have been easily visible on Earth, but was only barely visible by Flamsteed in 1680 because it was so dusty. A more reasonable approach is to look at various elemental abundances.
    – KAI
    Dec 5, 2016 at 17:13
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    creationists can believe in trigonometry, as long as they don't believe in the speed of light. Of course if you believe in a pre-gallilean universe model you believe that all objects in the night sky are merely projections on a fixed distance black sphere.
    – jwenting
    Dec 6, 2016 at 13:48

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