HUBBLE'S EXCITING UNIVERSE: FINDING SUPERMASSIVE BLACK HOLES

 Hubble’s sharp vision has helped astronomers solve a number of mysteries about supermassive black holes, including their abundance and their influence on galaxies in the evolving universe.

Einstein’s theory of general relativity first described the characteristics of such hypothesized gravitationally collapsed objects. His theory described an event horizon swallowing light, which would prohibit telescopes from ever directly seeing such objects.

The actual term “black hole” wasn’t coined until six decades later by astrophysicist John Wheeler. In the early 1970s, the first black-hole candidate, Cygnus X-1, was discovered in X-rays coming from superheated material swirling around a black hole orbiting a normal star. The black hole is 15 times the mass of our Sun.

In the early 1990s, Hubble began to provide compelling circumstantial evidence for the existence of gargantuan black holes measuring millions or billions of times the mass of our Sun. Because of Hubble’s ability to discern faint objects in the vicinity of bright objects, the telescope made definitive observations showing that quasars (very distant, compact sources of intense radiation) dwell in the cores of galaxies. These galaxies are greatly outshined by the quasar’s “floodlight-beam” brilliance. Hubble revealed that most of the galaxies were seen in the process of colliding with other galaxies, and, according to theory, these violent encounters would fuel a central black hole. Engorged with gas, the black hole loses some material to blazing jets that shoot out of a galaxy’s center like a blowtorch, which are easily resolved by Hubble.

Next, Hubble greatly bolstered the idea of supermassive black holes by measuring their masses, providing the first observational measurements that proved their existence. In 1997, Hubble astronomers looked at the nearest “mini-quasar,” the brilliant core of the giant elliptical galaxy M87. Astronomers used spectroscopy (dividing starlight into its component colors) to “weigh” a black hole to see if the amount of its unseen mass far exceeded the mass that could be attributed to stars alone. Hubble’s spectrograph measured the speed of gas trapped in the gravitational field of a black hole at the center. The extreme velocities indicated the presence of an ultra-compact central mass that could only be explained as a black hole.

The Hubble image on the left shows the core of the galaxy where the suspected black hole dwells. Astronomers mapped the motions of gas entrapped in the black hole’s powerful gravitational pull. The change in wavelength, or color, records whether an object is moving toward or away from the observer. The larger the excursion from the centerline—seen as a green and yellow along the center strip—the greater the rotational velocity. If no black hole were present, the line would be nearly vertical across the scan.

Astronomers used Hubble to measure the velocities at which stars and gas swirl around a black hole, to catalog black holes in active and quiescent galaxies. A Hubble census of galaxies showed that supermassive black holes are commonly found in a galaxy’s center. The survey suggests that black holes may have been intimately linked to the birth and evolution of galaxies. This idea is bolstered by a relationship, developed by Hubble observations, that a black hole’s mass is tied to the mass of a galaxy's central bulge of stars. The more massive the bulge, the more massive the black hole. This relationship implies there is some feedback mechanism between the growth of a galaxy and its central black hole.

NASA:Apophis asteroid Could Hit Earth in 2068.

 

Earth has been bombarded by space rocks throughout its history, but we’re lucky no large ones have slammed into the planet lately. Astronomers keep a careful watch on the skies, hoping to spot potential impactors far enough in advance that we can do something about it, and one of the most worrying objects is 99942 Apophis. This skyscraper-sized asteroid might still hit Earth in 2068, according to a new analysis from the University of Hawaii and NASA’s Jet Propulsion Laboratory. 

Scientists discovered Apophis in 2004, sounding the alarm when initial observations suggested it had a worryingly high 2.4 percent chance of hitting Earth in 2029. Thankfully, further study lowered that probability to zero. Still, astronomers have been keeping an eye on Apophis ever since — it’s currently considered the third-highest impact threat to Earth, behind 101955 Bennu and 29075 (1950 DA). However, the highest impact risks for those objects are centuries out. 

NASA’s Sentry Risk Table shows a 1 in 150,000 chance of Apophis hitting Earth in 2068, but that doesn’t take into account a phenomenon known as the Yarkovsky effect. As asteroids tumble through space, they absorb energy from the sun. That energy is radiated back into space as heat, but the process is not uniform over the object’s entire surface. The result is a small but measurable push that alters the object’s orbit. Davide Farnocchia at NASA and Dave Tholen from the University of Hawaii used data from the Subaru Telescope to try and pin down how much the Yarkovsky effect changes our odds. 

                                                        This is our best guess at Apophis’ shape.

Tholen says the true impact risk is probably closer to 1 in 530,000, a number used by the NEODyS impact monitor service that includes the Yarkovsky effect. The new observations will probably push NASA’s Sentry risk to a similarly low level. So yes, it’s probably less likely Apophis will hit Earth in a few decades, but astronomers will need to monitor its orbit over time to make sure. There is still a very real, non-zero chance that Apophis will get caught in Earth’s gravity in 2068. 

You don’t want to take any risks with an object like Apophis. While it’s not quite “mass extinction” big, an impact would be catastrophic. It’s a simple matter of physics — Apophis hitting Earth results in an explosion equivalent to 1,151 megatons of TNT. By comparison, the largest nuclear weapon ever detonated by humans was around 57 megatons. The 1883 eruption of Krakatoa clocked in at about 200 megatons. Apophis could level a small country, cause massive tidal waves, and spark widespread wildfires. All in all, a pretty bad day for Earth. 

In the event Apophis is ever on a collision course, astronomers should be able to tell us well in advance. Maybe it’ll even be early enough to try one of those pie-in-the-sky asteroid deflection systems we always hear about.

YouTube was down in India and other countries; Now back up: Know what happened

 

This widespread issue started at around 4 p.m. PT, with YouTube on Twitter confirming the problem. The company is “aware of the issue and working on a fix.” Given the timing, the outage is being particularly felt across the US.

YouTube on all platforms is currently browseable, but users are not able to play videos. Initially, the thumbnail image would appear on mobile, but be accompanied by a continuously loading progress indicator. Later on in the outage, an error message appeared. Searching for videos still works, but there is a slight delay before everything loads.

A similar issue plagues YouTube TV, which was only available in the US. The YouTube Music app does not appear to be impacted, but the streaming service was not loading on Smart Displays, speakers, or other Assistant devices.The Play Store was also affected. Android apps was downloading, but the install process failed.

The issue also affected YouTube TV and the movies and TV shows people purchase through Google TV. The platform was fixed after more than an hour.

DownDetector website showed severe user reported problems with YouTube, indicating the problem was widespread and numerous users on Twitter reported that YouTube wasn't working for them.

"If you're having trouble watching videos on YouTube right now, you're not alone and our team is aware of the issue and working on a fix. We'll follow up here with any updates," YouTube said in a tweet.

"...And we're back. We're so sorry for the interruption. This is fixed across all devices & YouTube services, thanks for being patient with us," YouTube said.

Earlier, the DownDetector graph peaked with more than 280,000 user reports in less than an hour.