Supernovae. A supernova is an explosion of a massive supergiant star. It may shine with the brightness of 10 billion suns! The total energy output may be 10^44 joules, as much as the total output of the sun during its 10 billion year lifetime ~ http://hyperphysics.phy-astr.gsu.edu/hbase/astro/snovcn.html

Using E=mc²

10^44 = m x 300000000 x 300000000

m = 10^44 / 9x10^16

m = 1.11 x 10^27 kg

That is more than the mass of 100 earth-sized planets. I don't think anything other than a blackhole can be dense enough to contain all that mass/energy in such small volume.

Supernovae. A supernova is an explosion of a massive supergiant star. It may shine with the brightness of 10 billion suns! The total energy output may be $10^{44}$ joules, as much as the total output of the sun during its 10 billion year lifetime. Using $E = mc^{2}$:

$10^{44}~\text{J} = m \cdot (300000000~\frac{\text{m}}{\text{s}})^{2}$

$m = \frac{10^{44}~\text{J}}{9 \cdot 10^{16}~\frac{\text{m}^{2}}{\text{s}^{2}}}$

$m = 1.11 \cdot 10^{27}~\text{kg}$

That is more than the mass of 100 earth-sized planets. I don't think anything other than a black hole can be dense enough to contain all that mass/energy in such small volume.