Mike Santoli, Senior Columnist for Yahoo FinanceMike is a Senior Columnist for Yahoo Finance, where he writes, analyzes and comments on the economy, the stock markets and corporate news.

He has covered Wall Street for 20 years, including 15 years as a columnist and feature writer for Barron’s magazine.

He is a regular on-air contributor to CNBC and a frequent guest on other cable and broadcast news programs.

(The following is food for thought from Mike’s latest post)  Never mind Hong Kong protests, Pimco’s palace intrigue or violent clashes in the Middle East. The crucial influence on our markets now is what investors are willing to pay for junk.

The high-yield, or junk bond, market has been the pounding heart of the bull market, pumping the cheap liquidity created by central banks through the corporate economy, attracting billions from income-parched investors, enabling generous corporate share buybacks and making stocks look attractive in comparison.

That’s why the recent bout of nervous selling in high-yield debt has got the stock market fibrillating in the six trading days since the Standard & Poor’s 500 index hit an all-time high a week ago Friday.

The junk-bond spread is the amount of extra yield investors demand above Treasury securities to compensate for the risk lower-rated issuers might default. This spread, while still quite tight versus history, weakened to its widest levels of the year Friday, according to bond strategists at RBS. At 4.62 percentage points above comparable Treasuries, the spread was up substantially from 4.08 points at the end of 2013.

Arranged by Gehr Brown