# In terms of power delivered to Earth, what is the brightest object in the sky?

I was reading about TXS 0506+056, a distant blazar. The Wikipedia article mentions it is one of the brightest objects in the sky at both gamma and radio frequencies. This got me wondering — if we consider brightness in terms of total energy delivered to Earth, which astronomical object is the brightest?

I can find vague-ish almost-answers to this, but only for specific frequency ranges (e.g. Object X is rather bright at Y MHz, but incredibly dim anywhere else, etc.) and only for photons. I am interested in any mechanism of energy delivery (cosmic rays, photons, gravitational waves, etc.); although, I would imagine photons probably account for the majority.

Let us also say that the energy doesn't have to be absorbed, so that forms of energy to which the Earth is more-or-less transparent (e.g. neutrinos) are okay too.

You can define "source object" however you wish. Transient events are okay too. If you want to give numbers, flux densities at Earth or a total power integrated over its cross-section would be welcome.

The obvious answer here in the Sun, so we shall exclude it. I suspect that the Moon and maybe some planets will also be contenders, so let’s just constrain ourselves to extrasolar sources. Consider this the only constraint on candidates.

• I presume you are excluding the Sun ? What else are you excluding ? Is there a minimum distance or a period that's relevant ? There might be events in the past that would qualify and we have either documented historical evidence for or have some scientific evidence for. Oct 11, 2020 at 8:14
• Great point — edited to reflect. Oct 11, 2020 at 8:15
• Interesting question indeed. Just one follow-up question to clarify. Since power is energy per time, $P = E/t$, I guess we have to define a certain unit time scale $t$ as base of comparison: A GRB may have a huge energy ($\sim 10^{44} {\rm J}$ if you trust Wikipedia), but lasts only seconds, so for short $t$, GRB would always win, but are luckily have not been observed yet on Earth. Feb 18, 2021 at 8:31