Starship Asterisk*

A Candidate for the Biggest Boom Yet Seen

Explanation: It is a candidate for the brightest and most powerful explosion ever seen -- what is it? The flaring spot of light was found by the All Sky Automated Survey for Supernovae (ASASSN) in June of last year and labelled ASASSN-15lh. Located about three billion light years distant, the source appears tremendously bright for anything so far away: roughly 200 times brighter than an average supernova, and temporarily 20 times brighter than all of the stars in our Milky Way Galaxy combined. Were light emitted by ASASSN-15lh at this rate in all directions at once, it would be the most powerful explosion yet recorded. No known stellar object was thought to create an explosion this powerful, although pushing the theoretical limits for the spin-down of highly-magnetized neutron star -- a magnetar -- gets close. Assuming the flare fades as expected later this year, astronomers are planning to use telescopes including Hubble to zoom in on the region to gain more clues. The above-featured artist's illustration depicts a hypothetical night sky of a planet located across the host galaxy from the outburst.

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This is an incredibly fantastic supernova, and I wish I had time to say more about my own thoughts about it. Maybe later. But I note that APOD Robot hints at the possibility that the light of ASASSN-15lh might have been beamed our way.

As a color commentator, I am of course extremely interested in the relative color of this supernova. All ultraluminous supernovas so far have been strikingly blue in color. If ASASSN-15lh really was as luminous as it appears to have been, it should have been remarkably blue and ultraviolet too. Does anyone know if this was the case?

Ann

I wonder why the sky of this planet stays so perfectly black. On earth even the light of the full moon masks many stars. Wouldn't a supernove do something similar? Is it just that the featured picture was taken high above the weather?

X&R wrote:I wonder why the sky of this planet stays so perfectly black. On earth even the light of the full moon masks many stars. Wouldn't a supernova do something similar? Is it just that the featured picture was taken high above the weather?

From the POD explanation.

The above-featured artist's illustration depicts a hypothetical night sky of a planet located across the host galaxy from the outburst.

Space artists love multiple huge disks of moons and planets in the sky of their drawings. I enjoy trying to figure out if the scene could depict stable orbits or is something exciting about to happen like a collision, ejection or maybe rings are about to be made. Usually the orbiting bodies are shown so huge that tidal heating would make them molten, but this drawing could show a stable system. Here's my guess. The small moon on the left orbits our vantage point, a large moon, and both orbit the Jupiter sized gas giant on the right. I'm also curious here about where the star is that these moons and planet orbit. The only lighting seems to come from the distant supernova.

It's a silly image. Not a whole lot of thought went into it. In other words, it's just for fun and to catch your eyes and try to get you to read the text.

I question any article that uses words like "kablooie". What I would like to read about are the error limits around the distance to this object. If that is not reliable or at all in question, the scenario is very different.

paulslittlebit wrote:

X&R wrote:
I wonder why the sky of this planet stays so perfectly black. On earth even the light of the full moon masks many stars. Wouldn't a supernova do something similar? Is it just that the featured picture was taken high above the weather?

From the POD explanation.

The above-featured artist's illustration depicts a hypothetical night sky of a planet located across the host galaxy from the outburst.

I was rather taken aback when Nitpicker related how unimpressed he was with (Supernova Type II) SN 1987A in the nearby Large Magellanic Cloud...a boring +2.9 magnitude star among hundreds of others. Now a LMC ASASSN-15lh would have been far more impressive: 5 magnitudes brighter or -2.1 magnitude... though it still would have been out-shined by Jupiter. To out-shine a full moon (as illustrated in the APOD picture perhaps) and really light up our night sky ASASSN-15lh would have be about as close as Deneb (at 800 parsecs).

Why are we given an "artist's impression"? That has to be no better that educated guesswork?
Why cannot this wonderful science website give us the actual image?

The link to the actual paper offers us a button for "Images and data" but as usual those are locked away behind an academic paywall.
Cannot even the prestigious Editors of APOD prise a picture out of the authors, perhaps bound by contract not to?

John

BIGGSLLOYD wrote:What I would like to read about are the error limits around the distance to this object. If that is not reliable or at all in question, the scenario is very different.

The distance value given is provided just to give a sense of scale. Scientifically, distance as such for cosmological objects like this is expressed as a redshift, which is very accurately measured (z = 0.2326). How this is converted to a distance depends both on how we define distance, as well as a set of assumed (but controversial or uncertain) parameters associated with the Big Bang cosmology (the Hubble constant, the Omega constants, whether the Universe is open or flat).

Assuming a flat universe and widely accepted values for the constants, the measured redshift means that the light has been traveling for 2.76 Ga, the comoving distance of the object is 3.1 Gly, and that the Universe was 10.8 Ga old (with a 13.565 Ga age) when the supernova occurred (or that it is currently that old in the reference frame of the observation).

Almost certainly, the different possible distance interpretations are reliable enough that our understanding of the actual intensity of this supernova has been realistically assessed.

JohnD wrote:Why are we given an "artist's impression"? That has to be no better that educated guesswork?
Why cannot this wonderful science website give us the actual image?

The link to the actual paper offers us a button for "Images and data" but as usual those are locked away behind an academic paywall.
Cannot even the prestigious Editors of APOD prise a picture out of the authors, perhaps bound by contract not to?

This is the only image found in the paper (and in fact, it isn't in the main paper, but only in the supplemental online material). All of the other figures are curves and diagrams that would not make for a very clear APOD (and arguably, this image might not be great for an audience as broad as APOD's). The image attached here was publicly offered in a press release, and is widely presented in more technical scientific news publications.

I agree with you about the artist's impression, which I also think is rather horrible (as are nearly all such renderings). But so it is. An APOD like this needs to be taken for the caption content, which is very good, and the image sort of ignored.

Two thoughts:
-- What is the spectrum like (un-red-shifted)?

-- Could this be something like the demise of a super massive "black hole" ?

Thanks.

I like Jin Ma's illustration and hope better days are ahead for their economic situation for everyone's sake. After things settle maybe the biggest boom is yet to come. It's interesting how astronomy interests have filtered to other facets of life.

I seems like, as in physics, probability plays a big part of our daily lives. I wish we could look back in time to see what the future actually held for us. Three billion years is a little too optimistic though. Thanks for the actual image Chris; I was curious how it appeared in this day and age.

dlw wrote:Two thoughts:
-- What is the spectrum like (un-red-shifted)?

Completely typical for supernovas:
Here compared with another supernova, showing the same shape and nearly identical (probably oxygen) absorption dips (a-d). The accompanying text describes the spectrum as "blue and featureless" (which may answer Ann's question above).

-- Could this be something like the demise of a super massive "black hole" ?

The paper does not list that as a scenario.

Thanks for the added details, which help me understand the actual observations. Nevertheless, I can see why the artist's illustration is a good choice to help spark our imagination of this -- the real data is just a blip by comparison. It is a most amazing event and observation. It seems that the high luminosity, while transient, is going to be around for years. Did I get that correctly? It probably still is the brightest such object (by luminosity) in our sky, and will drop something like one order of magnitude per year? If I understood correctly, based on what they eventually characterize the total output to be, then they could potentially rule out some source candidates, like a neutron star, for example. But then, as Ann noted, whether or not its radiation is directed in any way is a question that could make any estimates of total output into low-confidence guesses.

Thank you, Chris! Yes, rather undramatic, but when explained and the distance appreciated, more impressive.

dlw wrote: -- Could this be something like the demise of a super massive "black hole" ?
Thanks.

dlw,
I don't think BHs can 'demise', can they?
Even the final moments of a micro BH, going out in a blaze of Hawking radiation would be a candle next to this.

John

whoever is in charge of running the Universe, sure knows how to play in this sandbox

when APOD describes an event as " candidate for brightest " that doesn't mean visible light, does it ?

ta152h0 wrote:when APOD describes an event as " candidate for brightest " that doesn't mean visible light, does it ?

They are talking about the bolometric luminosity, a measure of total energy per unit time. We appear to be observing a blackbody with its peak in the UV or shorter, so most of the energy isn't in the visible spectrum. However, I think all of the extremely luminous phenomenon we know of are basically blackbodies, so if this is the most luminous over its entire output, it is also the most luminous just in the visible spectrum.

Is it possible this phenomenon should be categorized as more of a Quasar instead of a Super-nova?

The supernova looks pretty blue all right. It is very much bluer than its host galaxy, and its light is completely swamping the light from the host.

Clearly the light curve of this supernova peaks far in the ultraviolet part of the spectrum, as we would expect from an ultra-bright supernova.

Ann

I wonder if any associated GRB was detected?

[dlw] -- Could this be something like the demise of a super massive "black hole" ?
Thanks.

[John] -- dlw,
I don't think BHs can 'demise', can they?
Even the final moments of a micro BH, going out in a blaze of Hawking radiation would be a candle next to this.

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I'm not a physicist but I was assuming that a "black hole" that grew extremely large might become unstable is some way we've never imagined. It contains matter/energy in a state we can't observe (obviously) and in conditions that may be way outside our understanding of how matter/energy might behave. I was imagining something like an immense kind of fusion reaction that released energy beyond the gravitational force's ability to contain it.

I'm too lazy to look it up now, but I'm sure Hawking said that the bigger a black hole is, the longer it takes for it to annihilate itself. For a black hole of a few million solar masses, we are certainly talking about trillions of years.

And since the universe is only ~14 billion years, the chances of a million solar mass black hole destroying itself appears to be zero.

Ann