Supermassive black holes power some of the most luminous objects we see in the Universe. When material spirals into a supermassive black hole in the center of a galaxy that is in excess of a million Solar masses, it gives rise to an active galactic nucleus, or AGN (also discussed in two previous KIPAC blogposts: this one focused on observations of flaring from AGNs, whilethis one focused on simulation aspects). In addition to spewing electromagnetic radiation running from visible light through ultraviolet all the way to X-rays and gamma rays, many AGN can launch jets of particles at close to the speed of light. These jets are detected through the radio waves they emit by synchrotron radiation and can extend between 50 and 100 kpc (about 150,000 to 300,000 light years) from the central black hole. All this activity occurs in and around the so-called accretion disc: the flattened disc of gas that is spiralling into the black hole, just moments before it plunges through the surface of no return, the “event horizon” of the central massive black hole.
May 3, 2017 | They blinded it for science
Scientific introspection is necessary because of a known unknown in the world of experimentation called experimenter bias, the name given to all the ways in which simply being human can affect how scientists take data, analyze data, and interpret data. “Experimenter bias” is a known—i.e. it is well-known to exist—but it’s also unknown, because the psychology of the human scientist can’t be easily quantified. Researchers can’t add error bars indicating the strength of a preconceived notion or the weight of an unconscious desire, yet subtle and not-so-subtle influences definitely exist, such as the result of a previous experiment or the conclusion of a popular theory, and these influences can nudge a researcher into accepting a result prematurely or discounting results that don’t conform to expectation.
Last December, I travelled to the southernmost tip of the Earth to install a new camera on the South Pole Telescope (following a rich tradition of other KIPAC researchers who have travelled to Antarctica and returned to write about it, e.g. Val Monticue and Albert Wandui). This blogpost brings you along for a bit of that journey!
The high-energy universe is a fascinating place to observe: giant stars explode into supernovae, briefly outshining their own galaxies; pulsars with more mass than our Sun but only twelve miles across spin hundreds of times each second; and supermassive black holes at the centers of galaxies can suck dust and gas into accretion disks and blast this material in plasma form back out in powerful relativistic jets spewed out at close to the speed of light.
The H0LiCOW collaboration just released news that they’ve measured what KIPAC and H0LiCOW collaboration member Phil Marshall calls “a key property of the universe”: the Hubble constant, which tells how fast the universe is expanding. According to their measurements, our universe is currently expanding at 71.9 km/s/Mpc, within about 3.8% accuracy, which means that each second, our universe is adding very close to 71.9 kilometers of space per megaparsec in every direction. This expansion is increasing, a phenomenon attributed (for now, at least) to the influence of a new component of the universe, dark energy.
The acronym ΛCDM (Lambda-cold dark matter) is shorthand for our current best cosmological model describing the early beginnings, evolution until now, and future development of our entire Universe. It posits a cosmos dominated by a cosmological constant (denoted by Λ, the Greek letter capital lambda) our best guess for the phenomenon of dark energy, and a type of slow-moving, non-interactive matter called cold dark matter that outweighs the ordinary matter making up stars and planets—and us—by more than five to one. ΛCDM does well enough explaining the majority of our astrophysical observations that it is the standard paradigm for most people working in the field.
Some things just go together. Hot dogs and mustard, smart phones and selfies, school and summer vacation. But science is a year-round proposition, and several undergrads didn't seem to mind forgoing their summer vacations to pursue a variety of research opportunities with members of KIPAC. (Protip: it’s never too soon to start thinking about next summer!)
By modeling the warped images of a gravitational lens observed with one of the most powerful telescopes in the world, KIPAC scientists have made the dramatic discovery that there is a clump of dark matter with no currently visible normal-matter counterpart in a far-away galaxy. Such unaccompanied clumps are incredibly difficult to detect and only a small handful of them have ever been discovered, but a concerted effort to find them and determine how and why they form could pay off significantly in the long term by giving us new insights as to the nature of dark matter.
The first direct detection in 2015 of a gravitational wave event (GW) by the recently upgraded Laser Interferometer Gravitational-Wave Observatory, known as Advanced LIGO, ushered in with a mighty bang a completely new era in astronomy. The first science run with the Advanced LIGO detector started in September 2015, and two high-significance events (GW150914 and GW151226) and one sub-threshold event (LVT151012) were reported. These three events were compatible with signals expected from the mergers of two black holes.
The Crab Nebula, our old friend, has continued giving us big surprises in the past few years, as we recently saw in this KIPAC blogpost (from April 2015, by Jeff Scargle and Roger Blandford). We have been gaining glimpses into these surprises thanks to the excellent performance of the orbiting gamma-ray telescopes, Fermi and AGILE, which have been able to get glimpses into the hidden secrets kept mum for so long in other wavelengths by this old stalwart.
Jul 10, 2016 | Ripples in spacetime - from 1.3 billion light years away
By now most of you who are “astro-enthusiasts” have already heard the news originally announced in February 2016 of the gravitational wave event observed by Advanced LIGO in September 2015, and perhaps also heard a bit about how excited astrophysicists were about it. As for why we were all so enthused, maybe the simplest explanation is this: we have grown a new sense and have for the first time heard the ripples in spacetime emanating from two colliding black holes, spreading out throughout the Universe, and gently jiggling the Earth as they pass us by, in a way humans have never been able to before.
Jul 2, 2016 | Swift GRBs: a 3D step toward standard candles
Gamma-ray bursts (GRBs) are some of the most energetic events known in astrophysics. In just a few seconds, a typical burst can release as much energy as our sun will emit over its entire 10 billion-year lifetime so it is not surprising that GRBs have been detected billions of light years away. If the intrinsic brightness of GRBs were known, a comparison with their detected brightness would yield their effective distance, and given their observed recession velocity or redshift, GRBs could then be used as accurate distance estimators for cosmology. This would enable researchers to arrive at solid estimates for the distances of all manner of extremely faint, old objects, such as very early galaxies.