sunset from behind the wire

sunset from behind the wire

Monday, May 29, 2017

Stellar Death

I took the Ducati (She-Devil) out for a spin today on the highway, had breakfast at a road house overlooking a spectacular scene and started thinking about everything that was going on around us while I sat there eating over-medium eggs and a split English muffin. The Internet allows us to share more (good and bad) and thereby to see more.  You can't see a black hole because it sucks in light photons, but you can see the swirling, super heated gas that it's getting ready to eat (white dot in the center of what used to be a star, below). 

In the failed supernova of a red supergiant, the envelope of the star is ejected 
and expands, producing a cold, red transient source surrounding the newly 
formed black hole, as illustrated by the expanding shell (left to right). Some 
residual material may fall onto the black hole, as illustrated by the stream and 
the disk, potentially powering some optical and infrared emissions years 
after the collapse. Credit: NASA, ESA, P. Jeffries (STScI)
Are there 'white holes' in some distant dimension where matter is spewing out? I don't think that it works like that even though Sci-Fi writers like to ponder over such potential mysteries. 

In any event it's not just babies being born and people dying, people happy/people sad, but stellar birth and death that was going on while I slurped down the eggs, bacon and a couple slices of cantaloupe. For the first time in history, astronomers have been able to watch as a dying star was reborn as a black hole. The process happens quickly as the star loses cohesion. The photo sequence above took place over seven years. And while it's true that I'm not a slow eater. stuff does happen.
S. M. Adams, C. S. Kochanek, J. R. Gerke, K. Z. Stanek. The search for failed supernovae with the Large Binocular Telescope: constraints from 7 yr of data. Monthly Notices of the Royal Astronomical Society, 2017; 469 (2): 1445 DOI: 10.1093/mnras/stx898
The star, which was 25 times as massive as our sun, should have exploded in a very bright supernova. Instead, it fizzled out -- and then left behind a black hole.

"Massive fails" like this one in a nearby galaxy could explain why astronomers rarely see supernovae from the most massive stars, said Christopher Kochanek, professor of astronomy at The Ohio State University and the Ohio Eminent Scholar in Observational Cosmology.

As many as 30 percent of such stars, it seems, may quietly collapse into black holes -- no supernova required.

"The typical view is that a star can form a black hole only after it goes supernova," Kochanek explained. "If a star can fall short of a supernova and still make a black hole, that would help to explain why we don't see supernovae from the most massive stars."

He leads a team of astronomers who have been using the Large Binocular Telescope (LBT) to look for failed supernovae in other galaxies. They published their latest results in the Monthly Notices of the Royal Astronomical Society.

Among the galaxies they've been watching is NGC 6946, a galaxy 22 million light-years away that is nicknamed the "Fireworks Galaxy" because supernovae frequently happen there -- indeed, SN 2017eaw, discovered on May 14th, is shining near maximum brightness now. Starting in 2009, one particular star in the Fireworks Galaxy, named N6946-BH1, began to brighten weakly. By 2015, it appeared to have winked out of existence.

The astronomers aimed the Hubble Space Telescope at the star's location to see if it was still there but merely dimmed. They also used the Spitzer Space Telescope to search for any infrared radiation emanating from the spot. That would have been a sign that the star was still present, but perhaps just hidden behind a dust cloud.

All the tests came up negative. The star was no longer there. By a careful process of elimination, the researchers eventually concluded that the star must have become a black hole. It's too early in the project to know for sure how often stars experience massive fails, but Scott Adams, a former Ohio State student who recently earned his Ph.D. doing this work, was able to make a preliminary estimate.

"N6946-BH1 is the only likely failed supernova that we found in the first seven years of our survey. During this period, six normal supernovae have occurred within the galaxies we've been monitoring, suggesting that 10 to 30 percent of massive stars die as failed supernovae," he said.

"This is just the fraction that would explain the very problem that motivated us to start the survey."

To study co-author Krzystof Stanek, the really interesting part of the discovery is the implications it holds for the origins of very massive black holes -- the kind that the LIGO experiment detected via gravitational waves. (LIGO is the Laser Interferometer Gravitational-Wave Observatory.)

It doesn't necessarily make sense, said Stanek, professor of astronomy at Ohio State, that a massive star could undergo a supernova -- a process which entails blowing off much of its outer layers -- and still have enough mass left over to form a massive black hole on the scale of those that LIGO detected.

"I suspect it's much easier to make a very massive black hole if there is no supernova," he concluded.

They Guard the Streets

I love the Marines. I served in the Navy, but there is something special about the Marine Corps. Yes, they are naval infantry - but the sum is even greater than its parts. I was deployed to Ras Al Mishab (just across the border with Kwait not that far south of Qasr) during the First Gulf War with SEAL Team Five, Alpha Platoon and also worked with SEAL Delivery Vehicle Team One, Delta Platoon (embarked on the USS Curts FFG 38). While there, I we used to take chow with the Third BTN, First MarDiv, and it drove them nuts because none of us wore any identification at all beyond the standard camo uniform, and non-standard weapons and gear that we carried. I favored Lima Company because they liked L and I liked it twice as much as they did... We pranked the Marines mercilessly and they took it with stoicism -- usually.

Eventually they became accustomed to the Navy and tolerated us. Three or so months later, we set up our own galley ashore (better food). Sometimes Marines would join us for chow then, but they still never were sure who to salute. 

I have a thousand Marine stories. Almost all of them are testaments to the young men (and some women) who served honorably, and many of whom gave the last full measure of their devotion.

My commemoration of bravery, honor, sacrifice and duty on Memorial Day goes out to those brave souls of the Naval Service who guard the streets of heaven.