Search teams in the southern Indian Ocean have detected yet another signal that authorities hope is coming from the black boxes on Malaysia Airlines Flight 370.

That makes five distinct signals in just a few days, narrowing the search area even more for teams who have been combing the seas for more than a month.

"The acoustic data will require further analysis overnight but shows potential of being from a man-made source," said Australia's Air Chief Marshal Angus Houston, in reference to the most recent signal.

Thursday's search area is smaller — about 22,400 square miles, or roughly the size of West Virginia, as CNN notes — as teams think they're getting closer to what may be MH370's final resting place.

Image: Australian Maritime Safety Authority

This latest signal was picked up near the Australia's Ocean Shield ship that detected the other signals, which is significant because that means they're all coming from the same area.

Underwater search teams picked up two distinct signals yesterday: The first lasted 5 minutes, 32 seconds; the second was 7 minutes. They were within the confines of an area that's less than 1,500 miles from Perth.

Image: Australian Maritime Safety Authority

After this week's discoveries, authorities are growing more confident that they're zeroing in on Flight 370, which went missing on March 8 with 239 people on board.

"I'm now optimistic. We'll find the aircraft or what's left of the aircraft in the not too distant future," Houston said Wednesday.

After chasing down several dead-end leads over the past month, authorities approached the first rounds of signals with skepticism because marine life can sometimes emit similar sounds. However, experts analyzed the first two signals that were detected over the weekend and determined that they were, in fact, from a manmade device and not nature.

If teams recover the plane's black boxes, it will be nothing short of a miracle. For one, time isn't on their side. Batteries in the flight recorders last only 30 days. As of Thursday, the plane has been missing for 34 days.

Although the search area is now smaller, teams are still up against depths that plunge nearly 3 miles. To put that into perspective, just take a look at this Washington Post graphic.

Timeline of the search for MH370