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(CNN) -- Scientists have discovered a "monster black hole" so massive that, in theory, it shouldn't exist.It's a stellar black hole — the type that forms after stars die, collapse, and explode. Researchers had previously believed that the size limit was no more than 20 times the mass of our sun because as these stars die, they lose most of their mass through explosions that expel matter and gas swept away by stellar winds.This theory has now been toppled by LB-1, the newly-discovered black hole. Located about 15,000 light years away, it has a mass 70 times greater than our sun, according to a press release from the Chinese Academy of Sciences.The findings were published by Chinese researchers in the journal Nature on Wednesday."Black holes of such mass should not even exist in our galaxy, according to most of the current models of stellar evolution," said Liu Jifeng, head of the team that made the discovery. "LB-1 is twice as massive as what we thought possible. Now theorists will have to take up the challenge of explaining its formation."Scientists are now scratching their heads at how LB-1 got so huge.The Chinese team has proposed a number of theories. LB-1's sheer size suggests that it "was not formed from the collapse of only one star," the study said -- instead, it could potentially be two smaller black holes orbiting each other.Another possibility is that it formed from a "fallback supernova." This is when a supernova -- the last stage of an exploding star -- ejects material during the explosion, which then falls back into the supernova, creating a black hole.This fallback formation is theoretically possible, but scientists have never been able to prove or observe it. If this is how LB-1 formed, then we may have "direct evidence for this process" for the first time, the study said.LB-1 is not the biggest black hole ever discovered -- but it may be the largest of its kind. There are several types of black holes, and stellar black holes like LB-1 are on the smaller side, according to NASA. Supermassive black holes are much bigger -- they can be billions of times the mass of our sun.Scientists believe supermassive black holes may be connected to the formation of galaxies, as they often exist at the center of the massive star systems -- but it is still not clear exactly how, or which form first.Stellar renaissanceStellar black holes are believed to be commonly scattered across the universe, but they are difficult to detect because they do not normally emit X-rays -- only doing so when they gobble up gas from a star that has ventured close enough. They are so elusive that scientists have only found, identified, and measured about two dozen stellar black holes, the press release said.The researchers at the Chinese Academy of Sciences tried a different approach. Instead of looking for X-rays emitted by black holes, the team looked for stars that were orbiting some invisible object, being pulled in by its gravity.Their efforts paid off -- they soon spotted a giant star eight times heavier than the sun, orbiting around what turned out to be LB-1."This discovery forces us to re-examine our models of how stellar-mass black holes form," said David Reitze, a physicist at the University of Florida. In May, Reitze's team made its own breakthrough discovery -- observing the never-before-seen collision of a neutron star and a black hole, which sent out ripples in space and time.These twin discoveries -- the collision, and now LB-1 -- indicate that scientists are reaching "a renaissance in our understanding of black hole astrophysics," said Reitze in the press release.There have been several other discoveries over the past year that have added to this renaissance. In October, researchers discovered what they believe to be a new type of black hole, smaller than the other kinds. And earlier this week, astronomers discovered a black hole that is actually helping baby stars grow instead of destroying them. 3971

(KGTV) - Feeling good, San Diego? America’s Finest City is also one of the happiest cities in the U.S., a study shows. Major metropolitan areas were ranked by WalletHub on 31 indicators of happiness, including income growth, depression rates, and average leisure time. The indicators were used to create scores for emotional and physical well-being, income and employment, and community and environment. San Diego came in 18th overall. Although the city was in 8th place for well-being, the community score was 46, and income was 36. EXPLORING SAN DIEGO: Find great ways to enjoy San Diego with your familyOther San Diego County cities, Chula Vista and Oceanside, ranked 27th and 34th, respectively. The top scoring cities include:1. Plano, TX2. Irvine, CA3. Madison, WI4. Fremont, CA5. Huntington Beach, CADetroit was last, ranking 128th.RELATED: San Diego named a top food city by YelpThe study showed some regional trends for different happiness factors. Four of the cities with the lowest depression rates were in Florida. The top cities for adequate sleep were in the Midwest. But the city that never sleeps - New York - didn’t make the top five for inadequate sleep rates. That dubious honor was held by Detroit. 1227

(KGTV) — Does a 1.4 ton cow really live on a farm in Australia?Yes.“Knickers” is 6-foot 4-inches and towers over the other cows in the herd.Amazingly, he’s not the largest cow in the world. 197

(KGTV) - A workplace shooting at YouTube's San Bruno headquarters has left many local workers wondering, "what would I do?"Cody Perron, COO of the security firm Fidelis Global Group, said it initially comes down to two simple things every employee can do."Number one is maintain situational awareness, so anywhere you are whether it's public or your office space," Perron said. "If it's in public, be concerned with your surroundings and notice things that stand out, that are counter to normal activity in that environment. Same thing with your office space."RELATED: Federal agents search YouTube shooter's San Diego home, family's Menifee housePerron added that knowing the facility is also important."Second thing I would say is know your facility. So when you walk inside a facility, especially where you work, you should know where your entries and exits are. You should know your emergency action plans," said Perron.Perron leads participants through workshops to practice safety measures in case of a workplace shooting. In those classes, participants are taught how to assess their situation, barricade, and some basic takedowns.RELATED: Female shooters are rare. YouTube attacker joins short listAside from sitting through a three-hour class, he said his two points are things that can be practiced every day anywhere, like noticing people dresses or behaving in alarming ways."There are things you can apply every day when you walk into an environment," Perron said. "These are things you can practice every day, that sort of become second nature." 1587

(KGTV and CNN) - Former FBI Director James Comey warned that if President Donald Trump ever tries to fire special counsel Robert Mueller, then it would be the President's "most serious attack yet on the rule of law," and said that "it's possible" the Russians could have information on Trump that could be used to compromise him.The comments came during a wide-ranging, exclusive interview with ABC News chief anchor George Stephanopoulos. The media appearance is the first time Comey has sat for a televised interview since Trump fired him last year. It also kicks off a promotional tour that the former FBI director is embarking on to promote the release of his new book, "A Higher Loyalty."Take our poll about the interview: 735