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Tuesday
Feb012011

The Murmur of the Hidden Monster: Supermassive Black Hole in Andromeda Goes Bonkers (in 2006)


What’s the problem with black holes? Well, for one, if you go within their Schwarschild Radius, you become spaghettified. And they mess up spacetime. To extend the oft-quoted bowling-ball-on-a-mattress analogy, if the mattress had sheets on it, the black hole-bowling ball would do a lot more than wrinkle them. Right? RIGHT?

Well, also, don’t forget that BHs don’t produce light. In fact, the point of them is that they trap light, stuffing it down their gullets and clamping their teeth shut.

However, we do see light associated with BHs. Light that is an effect of processes caused by their gravity. It’s not visible light, though—it’s X-rays, gamma rays, radio waves, spraying around Schwarschild radius, inside which is the part that gives “black hole” its first name. iMAGE: Jets of emission from BH at the center of a galaxy.
Marscher et al., Wolfgang Steffen, Cosmovision
NRAO/AUI/NSF

We infer the existence of black holes from this energetic activity, as well as from the orbital behavior of objects near suspected black holes (see video).


But all we can do is infer. And while we can make our inferences as scientifically robust as possible, we can’t know. So while we are all, “Duh, of course there are supermassive black holes at the centers of galaxies—they’re the only things with enough density to have the orbital effect of making a whole galaxy rotate around them yet not take up much space. Haven’t scientists accepted this idea for decades?” papers still contain mealymouthed phrases like “galaxies with a stellar bulge are thought to harbor,” which is how the paper I’m talking about today begins. The paper, whose title I heart, is called “The Murmur of the Hidden Monster: Chandra’s Decadal View of the Supermassive Black Hole in M31,” and is written by Li, Garcia, Forma, Jones, Kraft, Lal, Murray, and Wang.

The suspected, alleged, supposed supermassive black holes (SMBHs) in the local universe are radiatively quiescent. This is in contrast to far-away (a.k.a. “older”) galaxies that have “active galactic nuclei” (AGN), in which stuff is always a-fallin’ into their SMBHs.

Galactic nuclei like ours and our neighbors’ are sometimes called LLAGN, or low-luminosity AGN, because not enough stuff is a-fallin’ in. The most famous LLAGN is our own, SgrA*, but our hometown hero is actually a bit strange. Rather than having a fairly constant luminosity, SgrA* bursts periodically in its X-ray, infrared, and radio emission. Its X-rays are sometimes 100 times brighter than at quiescence. This behavior is unusual for LLAGN.

SgrA* was alone in its awkward outbursts till now, when Li, et al., showed that M31*, the SMBH at the center of the Andromeda (M31) Galaxy, also flares up.

But before we talk about that, let’s talk about this supposed “black” “hole.”

Fact the first: We infer the mass to be 1.4x10^8 solar masses.
Fact the second: The center of M31 has a double-nucleus, which astronomers interpret as a set of old stars orbiting the SMBH, which is at the center of one nucleus.

The Double Nucleus of M31  
Credit: T. R. Lauer (KPNO/NOAO) et al., HST


Fact the third: Telescopes have detected X-rays and radio waves that are believed to be caused by processes going on around the SMBH.

Subfact: We believe this because the suspected SMBH, the Xes, and the radios are positionally correlated.
Subquestion: Does it disturb you that coincidence (meaning co-incidence, not “isn’t it a coincidence that we have the same birthday?”) is how we infer causality?

I feel okay about it, but I thought I’d check in with you.

Li, et al. (2009) found that the baseline emission from M31* was 1.2 x 10^36 erg/s, which may look like a large number but is actually much smaller than it could be for a black hole of this mass.

Because these astronomers wanted to see if, perhaps, M31* acted like the center of the Milky Way—if its brightness varied drastically, they analyzed archived data from the X-ray telescope Chandra (located in SPACE), from 1999-2010.

So what did the researchers find, in terms of variation, between the 90s and today? Did the SMBH finally stop wearing its Nirvana t-shirt?

  1. 1999-2006: Quiescence, constancy.
  2. 2006: Outburst! AH! 250 times as bright as quiescent state.
  3. 2006-2010: A more active state, with frequent, smaller-scale brightness variations and a baseline 23 times brighter than quiescence.

This SMBH is so like being in a relationship, am I right?

While outbursts (AH!) in most LLAGN are attributed to tidal disruption (i.e. a star coming close to the SMBH) (Rees, 1988), M31*’s outburst does not have the same qualities as those others. Mostly, it is 10^34 times less bright, proportionally. It does, however, look similar to the outbursts from SgrA*.

Inference: The M31* and SgrA* outbursts share the same physical cause because they have the same physical characteristics. Tada.

While you may not find the results of this study fascinating, what fascinates me is our inability to access the objects we’re studying. In almost every other field, you can smell or scan or spin or dissect or otherwise manipulate your material. Any number of investigative methods are at your disposal, and you can control situations and variables yourself.

In astronomy, however, the variables come to you, and you’re just lucky enough that space is big enough that chances are that something out there will suit your purposes. But you have to find it. And then all you can do is catch photons it lost a long time ago.

We can’t take a spaceship and measure the gravity around a black hole ourselves; we have to measure the effects of the gravity in order to find out what the gravity is. We can’t go make sure that spatial co-incidence is actually causal connectivity. We can’t send one person to M31* and one person to SgrA*, make them watch for millions of years, and then have them meet up to discuss the similarities of their observations.

No, we must wait. And use phrases like “it is reasonable to speculate that.”And it is, I do believe, reasonable to speculate that.

REFERENCES
ResearchBlogging.orgZhiyuan Li, Michael R. Garcia, William R. Forman, Christine Jones, Ralph P. Kraft, Dharam V. Lal, Stephen S. Murray, & Q. Daniel Wang (2011). The Murmur of the Hidden Monster: Chandra's Decadal View of the Supermassive Black Hole in M31 The Astrophysical Journal Letters, 728 (L10), 1-6 : 10.1088/2041-8205/728/1/L10

Li, Z; Wang, Q.D.; Wakker, B.P. 2009, MNRAS, 397, 148.
Rees, M.J. 1988, Nature, 333, 523.

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Reader Comments (2)

Are there any pictures of black holes anywhere?

February 2, 2011 | Unregistered CommenterBrooke N.

There are pictures of the high-energy jets that are caused by material spiraling along the BH's magnetic field. And pictures of stars orbiting *around* BHs.

http://chandra.harvard.edu/photo/category/blackholes.html

February 2, 2011 | Unregistered CommenterSarah Scoles

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