Anonymous Asked:
I feel a bit stupid asking this... But what's in the center of a galaxy ?

theformerastronomer:

astronomicalwonders:

First off, not a stupid question at all! In fact, it is a very good one that many astronomers have dedicated their lives to researching! I think I’ll start with our galaxy and the general case of galaxies.

Here is an image of the center of our milky way (we can only get this side-on view because we are viewing it from within):

image

In this photo, a supermassive black hole resides in the bright white area, right of the center. The black hole has been calculated to be about 4 million solar masses. Yes. You heard correctly, there is a supermassive black hole at the center of our galaxy. However, don’t panic.

image

The supermassive black hole is about 27 kilolightyears away and we are a long way from any harm it could cause us. This is actually a very normal thing about the universe we live in. It is theorized that there are supermassive black holes at the center of almost every large galaxy! Everywhere we look we find evidence of them in the orbits of stars around the centers of galaxies.

Some galaxies have special cases of black holes, known as quasars, at their center. Here is an artists impression of a quasar:image

Quasar’s and supermassive black holes, when viewed relative to galaxies, are members of objects known as active galactic nucleus (or AGN for short). AGN’s are the super dense regions at the center of galaxies that have abnormal luminosity (meaning they are super bright), and often emit light/radiation in all wavelengths of the electromagnetic spectrum. Galaxies with AGN’s are known as Active Galaxies. Our galaxy is considered an active Galaxy.

Here is a hubble image of an AGN at the center of Galaxy M87. Electromagnetic radiation is seen being emitted from a jet:

image

There is still very little known about the causes of these AGN’s, how they are formed from supermassive black holes and the intermediate stages of AGN’s and black holes. There are even galaxies that have no AGN’s and the stability of galaxies has been a big mystery for the past few years. There is still much that we can learn in this area.

Science doesn’t have all of the answers, and it may never have all of them. But Science has a way to figure out those answers. Someone once told me that younger scientists are able to make breakthrough discoveries because they don’t yet know what is impossible.

So I would like to tell you again, this was not a dumb question! I encourage you to continue to ask these questions! Thanks for the great ask.

"To find the truth, we need imagination and skepticism" - Carl Sagan, Cosmos: A Personal Voyage

Sources: Max Planck Institute for Astrophysics, NASA, Hubble images

There are a couple of inaccuracies in the answer that the astronomer in me can’t quite let go (AGN were my thing, back when this was my day job).

Supermassive black holes (SMBHs) in themselves are not considered AGN. The SMBH at the centre of the Milky Way is not currently accreting matter at any appreciable rate, so the Milky Way is not presently considered an AGN. It occasionally gobbles up a star, but there’s no evidence to suggest the presence of an accretion disc with associated radiative activity.

It’s more true to say that ‘every AGN has an SMBH’, because the current model for AGN requires one. The present model (which has a lot of evidence in its favour, although as with all extragalactic models there’s a lot of scatter), basically states that all AGN have fundamentally the same structure (SMBH, accretion disc, some more distant non-stellar material) and that the differences between the different types (quasar, Seyfert 1, Seyfert 2, etc) is due to accretion rate and viewing angle.

As far as ‘some galaxies not having AGN’ goes, at the moment the evidence is in favour of every galaxy with a bulge component having an SMBH, and therefore likely having been an AGN in the past if they are not currently. Galaxies with only disk components do not show evidence of SMBH, so current thinking is that the processes that shape the galactic bulge also strongly influence SMBH formation.

The babiest SMBH that we* know of is in NGC 4395, with a mass of a mere ~10^5 solar masses. NGC 4395 has an extremely small bulge component. I could go on about this AGN for days.

*that I know of, really. I only read astro-ph in my spare time these days.

To add a quick, fun addendum to theformerastronomer’s great additions/corrections, there’s debate at the moment as to whether AGNs trigger or suppress star formation in the rest of the host galaxy. To be brief, the radiation pressure/winds/unicorns coming from the super massive black hole is thought to have an effect on the rest of the galaxy but is it pushing gas and dust together to trigger star formation, or is it blowing all the material out of the galaxy (or something else) or is there no appreciable effect at all? This is one of those current big unknowns and can cause debates at the pub if you get people talking about it, like the (non-)existence of the “galactic main sequence” hohoho. 

Picture I took Friday Night and gif’ed up of Ursa Major/The Plough (full info on Flickr here). What’s the difference?Both The Plough and Ursa Major are asterisms. This is the name given to a group of stars joined together to create a pattern. Like many asterisms, there’s more than one way to draw the lines to form Ursa Major (Latin for “Larger Bear”), so don’t be surprised if you’ve seen something different out there.A constellation nowadays is one of 88 areas of sky with well-defined borders recognised by the International Astronomical Union (IAU), each named for an asterism they contain. Astronomical objects can be located by the constellation they’re in. Bode’s Galaxy (M81) and the Cigar Galaxy (M82) are both in the constellation Ursa Major, even though they’re not within the asterism itself (they’re located above the bear’s head).

Picture I took Friday Night and gif’ed up of Ursa Major/The Plough (full info on Flickr here). What’s the difference?

Both The Plough and Ursa Major are asterisms. This is the name given to a group of stars joined together to create a pattern. Like many asterisms, there’s more than one way to draw the lines to form Ursa Major (Latin for “Larger Bear”), so don’t be surprised if you’ve seen something different out there.

constellation nowadays is one of 88 areas of sky with well-defined borders recognised by the International Astronomical Union (IAU), each named for an asterism they contain. Astronomical objects can be located by the constellation they’re in. Bode’s Galaxy (M81) and the Cigar Galaxy (M82) are both in the constellation Ursa Major, even though they’re not within the asterism itself (they’re located above the bear’s head).

New Cloaking Device Could Hide Future Buildings from Earthquakes

unazukin210:

Woohoo! I have a new mini-article in The GIST. This one is about hiding buildings from earthquakes using metamaterials. Metamaterials are super cool. You’re going to love them.

Fermi Paradox solved by invoking zombies

Drake’s Equation predicts that there should be plenty of alien life out there, so why haven’t we encountered any yet?

After modifying Drake’s Equation to take into account the likelihood of Spontaneous Necro-Animation Psychosis (SNAP), Kane and Zelziz find that, alarmingly, we’re very likely to encounter the undead amongst the stars. Thankfully however, they provide a method to detect zombie planets from the composition of the atmosphere, reducing the threat to human explorers. 

CERN to switch to Comic Sans

From today, all of CERN’s official communication channels are switching to exclusive use of the font Comic Sans. The move comes after weeks of deliberation by CERN management and top web designers about how best to update the image of the laboratory for this, its 60th anniversary year.  
"This is an important year for CERN and we wanted to make a bold visual statement," says CERN Head of Communications James Gillies.

(Source: astronemma)

purestformofexpression:

The first identified compact galaxy group, Stephan’s Quintet is featured in this remarkable image constructed with data drawn from Hubble Legacy Archive and the Subaru Telescope on the summit of Mauna Kea. The galaxies of the quintet are gathered near the center of the field, but really only four of the five are locked in a cosmic dance of repeated close encounters taking place some 300 million light-years away. The odd man out is easy to spot, though. The interacting galaxies, NGC 7319, 7318A, 7318B, and 7317 have a more dominant yellowish cast. They also tend to have distorted loops and tails, grown under the influence of disruptive gravitational tides. The mostly bluish galaxy, NGC 7320, is in the foreground about 40 million light-years distant, and isn’t part of the interacting group. Still, captured in this field above and to the left of Stephan’s Quintet is another galaxy, NGC 7320C, that is also 300 million light-years distant. Of course, including it would bring the four interacting galaxies back up to quintet status. Stephan’s Quintet lies within the boundaries of the high flying constellation Pegasus. At the estimated distance of the quintet’s interacting galaxies, this field of view spans over 500,000 light-years.

purestformofexpression:

The first identified compact galaxy group, Stephan’s Quintet is featured in this remarkable image constructed with data drawn from Hubble Legacy Archive and the Subaru Telescope on the summit of Mauna Kea. The galaxies of the quintet are gathered near the center of the field, but really only four of the five are locked in a cosmic dance of repeated close encounters taking place some 300 million light-years away. The odd man out is easy to spot, though. The interacting galaxies, NGC 7319, 7318A, 7318B, and 7317 have a more dominant yellowish cast. They also tend to have distorted loops and tails, grown under the influence of disruptive gravitational tides. The mostly bluish galaxy, NGC 7320, is in the foreground about 40 million light-years distant, and isn’t part of the interacting group. Still, captured in this field above and to the left of Stephan’s Quintet is another galaxy, NGC 7320C, that is also 300 million light-years distant. Of course, including it would bring the four interacting galaxies back up to quintet status. Stephan’s Quintet lies within the boundaries of the high flying constellation Pegasus. At the estimated distance of the quintet’s interacting galaxies, this field of view spans over 500,000 light-years.

(via astronomicalillusion)

Media Advisory: Press Conference in Brazil to Announce Discovery in Outer Solar System

I’ve been doing a lot of “expecting news” news recently but oh well - 

There’s been a discovery in the Outer Solar System! “This unexpected result raises several unanswered questions and is expected to provoke much debate”. Press conference will be at 17.30UTC tomorrow. 

Irritatingly, I can see on a FB thread that a lot of other astronomers have read the embargoed press release and say it’s gonna be a good one but are keeping quiet on the exact contents, grrr. 

I’m close to betting money that it’s something to do with Pluto - what else in the Outer Solar System provokes a lot of debate? Either that or a Mass Relay (#masseffectjoke)

Any guesses before we find out?

My observing run to JCMT, Hawai’i’s been confirmed for 25th of May to 1st of June which means I can start booking, and I want to make good on my promise to keep you up to date on the entire experience… Anyone want to know about the paperwork? 

BICEP2 detects imprint of primordial gravitational waves in Cosmic Microwave Background

parkysnewbrain:

The science team working for the BICEP2 (Background Imaging of Cosmic Extragalactic Polarization) experiment have released their results. These show a statistically significant detection of B-mode polarization (the pattern of linear polarization is gradient-free, possessing only “curl” or…

Parky is an actual cosmologist, so have a read, guys! ^^