Two new tidal disruption events discovered

Two new tidal disruption events discovered
Artist's impression of a tidal disruption event. Image credit: ESA/C. Carreau

In two recently published scientific papers, an international team of astronomers has presented the detection of two new tidal disruption events (TDEs). Using the Palomar Observatory located near San Diego, California, the researchers discovered flares of radiation which turned out to be TDEs. Their findings were described in papers published online March 2 and 3 on the arXiv pre-print server.

TDEs are astronomical phenomena which occur when a star passes close enough to a supermassive black hole and is pulled apart by the black hole's tidal forces, causing the process of disruption. Such tidally disrupted stellar debris starts raining down on the black hole and radiation emerges from the innermost region of accreting debris, which is an indicator of the presence of a TDE.

For astronomers and astrophysicists, TDEs are potentially important probes of strong gravity and accretion physics, providing answers about the formation and evolution of supermassive .

The first TDE identified in the 1990s took the form of luminous soft X-ray outbursts in quiescent galaxies from the ROSAT survey. More recent TDE discoveries were made by surveys like the intermediate Palomar Transient Factory (iPTF), which utilizes the 1.2-meter Samuel Oschin Telescope at Palomar Observatory. Now, a team of astronomers reports another detection of TDEs from the iPTF survey.

The newly found TDEs were spotted on May 29 and Aug. 29, 2016 and designated iPTF16axa and iPTF16fnl respectively. A series of follow-up observations using NASA's Swift space observatory and ground-based telescopes was also conducted to gain insights into the evolution of these two events.

The researchers found that iPTF16axa was detected 49 rest-frame days after disruption. They discovered that its light curve shows no color evolution with time and has a constant temperature of about 30,000 K. They also found that this TDE is hosted by a Sloan Digital Sky Survey (SDSS) galaxy with an estimated black hole mass of approximately 40 million solar masses – one of the highest black hole masses among TDE hosts known to date.

The data provided by Swift allowed the team to exclude the possibility that the detected flare of radiation could be caused by a variable active galactic nucleus (AGN) and confirmed that it originated from a TDE.

"Both Swift UVOT observations and the follow up spectra of iPTF16axa are consistent with the object being a TDE rather than a supernova or a variable AGN," the paper reads.

Moreover, the research indicates that the massive black hole and the short rise time suggest that general relativity effects might play an important role in this event.

In contrary to iPTF16axa, iPTF16fnl is hosted by a galaxy (designated Markarian 950) with a much less – about two million solar masses. It is the lowest black hole mass in TDE hosts among the optical sample of TDEs. The team also noted that iPTF16fnl shows very strong emission in ultraviolet wavelengths, with a temperature of about 19,000 K. They added that this TDE is very unusual when compared to other such events.

"iPTF16fnl is remarkable in three ways: it is the nearest well studied TDE (66.6 Mpc), and it has one of the shortest exponential decay timescales (about 15 days) and one of the lowest peak luminosities," the researchers wrote.

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Mar 09, 2017
This comment has been removed by a moderator.

Mar 09, 2017
We are all SO irrelevant, . . .

A truism but an irrelevant one.

We exist in the here and now. It is up to each of us to create our own relevance. Which I opinionate is defined by our interactions with everyone else and the world we occupy.

To quote Larry Niven: "When our situation is hopeless, it is useless to give up!

Mar 09, 2017
"When our situation is hopeless, it is useless to give up!"

Yup, you either fight to the end, . . . . . or party!!

Mar 09, 2017
Very interesting. Also quite impossible to explain without black holes; no other force is strong enough in the aggregate to rip a star apart but gravity. And if it's strong enough to rip a star apart, the strength must grow, by the inverse square law, to be great enough to stop light.

I mean, you don't have to call that a black hole if it makes you feel all twitchy, but at least come up with some other name for it. And whatever you call it, relativity predicted it a hundred years ago. So good luck with that.

Mar 10, 2017
I've always heard that gravity is quite weak.

Mar 10, 2017
I've always heard that gravity is quite weak.
On a local scale, compared with the other forces, yes it is. But the thing about gravity is that unlike the other three, there's no negative gravity, so it just builds up and builds up as you add more and more matter and energy, whereas you're just adding both more negative and more positive to the others, which amounts to nothing. So ultimately, over the widest scales, it's the strongest.

Mar 10, 2017
I've always heard that gravity is quite weak.

I bet you wouldn't believe it if you are skydiving and you suddenly realize you've forgotten your parachute.

Mar 10, 2017
I've always heard that gravity is quite weak.

...which is the reason why it's the dominant force at large scales.

Think about it: let's say you have another force that is much stronger (e.g. the force between positive and negative electrical charges). Those charges would want to get on top of each other ASAP and would accelerate incredibly fast to do so*
That's why you don't find any really large scale differences in charge out there. So gravity remains the only force active at the longest ranges (unless there's an even weaker force we haven't discovered yet).

*The reason why the charges don't get even more on top of one another - i.e. why the positive charges accumulate in the nucleus and the electrons in a cloud around it - have to do with the other forces and the uncertainty principle.

Mar 15, 2017
I have a question, I was wondering if anyone had a possible answer to.

My understanding of Gravitational Force is that the difference from other Fundamental Forces is, that Gravity is a one-way attractor. Always inward to the center of mass.
And that two such masses, when close enough to one another, the respective attractors (cancel?) (interfere?) (diffuse? ) (detract?) (reduce?) their overlapping fields of attraction?

Yet the one-gee of Earth does not reduce or replace the 1/6th gee of Luna? Even though our moon is a siamese-twin with the larger planet?

Why isn't there a combining of the two gravitational fields? Instead of (evidently?) a (nullification?)

Mar 15, 2017
@willis, tides show the influence of the Moon; on the near side of the Earth, the oceans are pulled more by the Moon and on the far side they are pulled less. This shows both the influence of the Moon on the Earth's matter, and the inverse square law.

You really need to learn some physics if you're going to talk about gravity.

Mar 16, 2017
@willis, tides show the influence of the Moon; on the near side of the Earth, the oceans are pulled more by the Moon and on the far side they are pulled less.

Actually the oceans bulge out on the near and the far side.
"The ocean surface moves because of the changing tidal equipotential, rising when the tidal potential is high, which occurs on the parts of the Earth nearest to and furthest from the Moon."


Mar 16, 2017
Why isn't there a combining of the two gravitational fields?

The gravitational field is the superposition of all the fields out there (Earth, Moon, Sun, Jupiter, any grain off dust in the cosmos, the guy next to you, ... ). But since the force drops off with the radius squared the effect of sources that are far away (e.g. some comet in the Oort cloud) don't amount to much. Neither do sources that have little mass - though distance gets to be the deciding factor pretty fast. E.g. at birth a mother has a greater gravitational attraction towards her baby than Jupiter does. Her mass is much smaller but she's a lot closer (there's a "Yo momma" joke in there somewhere).
So much also for astrology and the 'influence of the planets at birth'. The constellation between you and the people in the room has more influence.

The Moon and the Sun do noticeably affect tides (as mentioned by others). You even do get measurably higher/lower tides when Sun, Earth and Moon are aligned.

Mar 16, 2017
"You really need to learn some physics if you're going to talk about gravity."

Dear Da Schneib, thank you for your advice. However I am an antiqued philosopher and do lack rigorous scientific education.

I appreciate that this community of commentators are willing to try to explain, what is actually mathematics, in concepts simple enough for me to muddle through.

I admit my ignorance. However, if I was too cowardly to admit my ignorance? I would also be revealing that I am stupid.

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