Sky & Telescope - April 2023 - 38
ESO / M. KORNMESSER
Novae
DANGEROUS DANCE In a nova
system, a white dwarf siphons material
from a companion star (here, a red giant).
The material piles up on the white
dwarf's surface until it's so hot and
dense that it erupts in a nuclear blast.
May 2022, p. 20) and another 20% from the same interstellar
crossfire that created Earth's beryllium. Much of the rest,
however, probably came from novae. So if lithium-ion batteries
power your cell phone or your electric car, you can thank
the hard work of numerous novae.
For a long time, though, no one saw any lithium in novae,
and some scientists even doubted that novae made the element.
Nevertheless, Matteucci says nonexploding stars hold
a vital clue: Most old stars have equally low levels of lithium,
while young stars have much more. Thus, something has
made lithium during the lifetime of the galaxy, steadily
enriching the interstellar gas that forms stars. Moreover,
the uniformly low lithium level among old stars means the
source is something that took a while to get its act together -
in other words, something like novae.
Then, in 2013, two different astronomical teams saw the
creation for themselves.
Element of Surprise
Akito Tajitsu (National Astronomical Observatory of Japan)
and his colleagues pointed the Subaru Telescope at a nova
in Delphinus, detecting spectral lines at difficult-to-observe
near-ultraviolet wavelengths. " The beryllium-7 absorption
was very strong, " he says. " The amount we observed was
about 10 times larger than the theoretical expectation. That
was really a surprise for us. "
The beryllium must have decayed into lithium. " This is
the first clear evidence that lithium is produced in a nova
explosion, " says team member Wako Aoki (National Astronomical
Observatory of Japan). " I was quite surprised and
very excited. "
38 APRIL 2023 * SKY & TELESCOPE
So unexpected was the beryllium-7 discovery that the
Japanese astronomers didn't publish it until two years later.
Meanwhile, a team led by researchers in Italy observed
another nova. Peaking at third magnitude, Nova Centauri
2013 was the brightest nova of the 21st century so far.
" It was very surprising, " says Luca Izzo (now Niels Bohr
Institute, Denmark), who detected not beryllium but neutral
lithium in the blast. A nova should strip each lithium atom
of the electron that makes the red spectral line the astronomers
observed. Nevertheless, they saw much more lithium in
the nova than theory predicted, just as the Japanese had seen
much more beryllium. Izzo's team also waited two years to
publish the finding.
Since these discoveries, both teams have detected beryllium-7
in many more novae. Izzo's team even saw beryllium-7
in two novae that appeared in another galaxy, the Small Magellanic
Cloud, in 2019 and 2020 as well as in RS Ophiuchi, a
recurrent nova in the Milky Way that exploded in 2021.
So just how much of Earth's lithium-7 came from novae?
Tajitsu estimates about 50%. Izzo says about 70%. Matteucci
thinks about 75%. Aoki estimates 70% to 80%. Starrfield
says about 90%. If these scientists are right, about half or
more of the lithium in your cell phone was forged in nova
explosions in the galaxy.
Oh, the irony! This is the most fragile of all naturally
occurring chemical elements. The protons and neutrons in
the nucleus of its dominant isotope are more weakly bound
to one another than is the case for any other element. Yet
lithium owes much and perhaps most of its existence to the
violence of a nuclear explosion. It's as if an atomic bomb
somehow spawned the most delicate of flowers.
Sky & Telescope - April 2023
Table of Contents for the Digital Edition of Sky & Telescope - April 2023
Contents
Sky & Telescope - April 2023 - Cover1
Sky & Telescope - April 2023 - Cover2
Sky & Telescope - April 2023 - 1
Sky & Telescope - April 2023 - Contents
Sky & Telescope - April 2023 - 3
Sky & Telescope - April 2023 - 4
Sky & Telescope - April 2023 - 5
Sky & Telescope - April 2023 - 6
Sky & Telescope - April 2023 - 7
Sky & Telescope - April 2023 - 8
Sky & Telescope - April 2023 - 9
Sky & Telescope - April 2023 - 10
Sky & Telescope - April 2023 - 11
Sky & Telescope - April 2023 - 12
Sky & Telescope - April 2023 - 13
Sky & Telescope - April 2023 - 14
Sky & Telescope - April 2023 - 15
Sky & Telescope - April 2023 - 16
Sky & Telescope - April 2023 - 17
Sky & Telescope - April 2023 - 18
Sky & Telescope - April 2023 - 19
Sky & Telescope - April 2023 - 20
Sky & Telescope - April 2023 - 21
Sky & Telescope - April 2023 - 22
Sky & Telescope - April 2023 - 23
Sky & Telescope - April 2023 - 24
Sky & Telescope - April 2023 - 25
Sky & Telescope - April 2023 - 26
Sky & Telescope - April 2023 - 27
Sky & Telescope - April 2023 - 28
Sky & Telescope - April 2023 - 29
Sky & Telescope - April 2023 - 30
Sky & Telescope - April 2023 - 31
Sky & Telescope - April 2023 - 32
Sky & Telescope - April 2023 - 33
Sky & Telescope - April 2023 - 34
Sky & Telescope - April 2023 - 35
Sky & Telescope - April 2023 - 36
Sky & Telescope - April 2023 - 37
Sky & Telescope - April 2023 - 38
Sky & Telescope - April 2023 - 39
Sky & Telescope - April 2023 - 40
Sky & Telescope - April 2023 - 41
Sky & Telescope - April 2023 - 42
Sky & Telescope - April 2023 - 43
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Sky & Telescope - April 2023 - 45
Sky & Telescope - April 2023 - 46
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Sky & Telescope - April 2023 - 48
Sky & Telescope - April 2023 - 49
Sky & Telescope - April 2023 - 50
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Sky & Telescope - April 2023 - 84
Sky & Telescope - April 2023 - Cover3
Sky & Telescope - April 2023 - Cover4
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